# Physics help

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Thread starter 3 years ago
#1
Hello,

I was wondering if anyone could do these tasks for me on the document that I've attached for physics with the working out possibly so that I can understand it? Or even one of the tasks maybe? It'd be really appreciated if you could!

Ak
0
3 years ago
#2
The tasks all revolve around heat energy and specific heat capacity/latent heat so I urge you to read up from your textbook/handout before attempting the questions. I'm not going to answer all the tasks but here's the 2nd one and the others are quite similar.
1. The catch in this question is that there are 2 equations involving specific heat capacity because the melting point of zinc will be crossed when changing it from solid to liquid. So first you need to convert the celcius values to kelvin by adding 273 to them. The main equation for specific heat capacity is: heat energy= mass x specific heat capacity x (difference in temperature)
So there are 2 sets of (difference in temp.) one before reaching melting point and one after. Here's the calculation:
K = C + 273. 20 C= 293 K and 550 C= 823 K
first difference in temp= 692-293=399 K
second difference in temp= 823-692=131 K

heat energy (1)= mass x specific heat capacity of solid zinc x 399
heat energy (2)= mass x specific heat capacity of liquid zinc x 131
heat energy (3)= mass x latent heat of fusion

Sum of the 3 is your answer.

2. Energy efficiency = energy output / energy input x 100
The previous answer is the output. Substitute values in the equation to get the answer.

3. 15 min x 60= 900 seconds
Power= energy/time so the first answer divided by 900 will give you the answer in Watts.

Watch out for the values given in kJ is 1000 J.

If you have more specific doubts in other questions, let me know.

Hope this helps
0
Thread starter 3 years ago
#3
(Original post by Nikita Verma)
The tasks all revolve around heat energy and specific heat capacity/latent heat so I urge you to read up from your textbook/handout before attempting the questions. I'm not going to answer all the tasks but here's the 2nd one and the others are quite similar.
1. The catch in this question is that there are 2 equations involving specific heat capacity because the melting point of zinc will be crossed when changing it from solid to liquid. So first you need to convert the celcius values to kelvin by adding 273 to them. The main equation for specific heat capacity is: heat energy= mass x specific heat capacity x (difference in temperature)
So there are 2 sets of (difference in temp.) one before reaching melting point and one after. Here's the calculation:
K = C + 273. 20 C= 293 K and 550 C= 823 K
first difference in temp= 692-293=399 K
second difference in temp= 823-692=131 K

heat energy (1)= mass x specific heat capacity of solid zinc x 399
heat energy (2)= mass x specific heat capacity of liquid zinc x 131
heat energy (3)= mass x latent heat of fusion

Sum of the 3 is your answer.

2. Energy efficiency = energy output / energy input x 100
The previous answer is the output. Substitute values in the equation to get the answer.

3. 15 min x 60= 900 seconds
Power= energy/time so the first answer divided by 900 will give you the answer in Watts.

Watch out for the values given in kJ is 1000 J.

If you have more specific doubts in other questions, let me know.

Hope this helps
Thanks so much for your help!!!! You're a real life saver!!
I've tried doing it all - I was wondering if you could tell me if these answers are correct for each of those questions:
1) 11974310 J
2) 20645362.07 J (especially this one as I just thought that this value seemed a bit too high?)
3) 13304.79 W

Also please could you do all the rest of the tasks for me by any chance, as I really need it done by Monday for my teacher and I'm not understanding any of the books Or if not all the rest, just task 1 and 3? Please? I did have a try at task 1, but my teacher told me it was wrong and won't give me help on it and I also tried task 3 and I just don't know how to start it at all
0
3 years ago
#4
(Original post by Ak786454)
Thanks so much for your help!!!! You're a real life saver!!
I've tried doing it all - I was wondering if you could tell me if these answers are correct for each of those questions:
1) 11974310 J
2) 20645362.07 J (especially this one as I just thought that this value seemed a bit too high?)
3) 13304.79 W

Also please could you do all the rest of the tasks for me by any chance, as I really need it done by Monday for my teacher and I'm not understanding any of the books Or if not all the rest, just task 1 and 3? Please? I did have a try at task 1, but my teacher told me it was wrong and won't give me help on it and I also tried task 3 and I just don't know how to start it at all
You're most welcome, I'm glad I could help.

You're answers are absolutely correct. The second value appears high because we have converted all values to Joules instead of keeping them in kJ. If you divide by 1000 to convert it, it may not seem so high after all.

Sure, I'll help you. I'll explain the other tasks which will also help you answer task 4, Once again, I won't give you the working or answers directly because that will be of no help; you need to understand the concept so you can attempt any questions on this topic.

Okay so task 3 is somewhat a reverse of task 2. One thing to keep in mind is that heat energy, the amount or value of it remains the same- you can input a certain amount of heat energy to raise something by a certain temperature and you can remove the same amount of heat energy to cause the same reduction in temperature. This is why the formula remains the same irrespective of whether the mass in question is being heated or cooled. So we heated Zinc in task 2 and now we're cooling water in task 3. Same formulae.

Just like task 2, the temperature difference (from 140C to 50C) the question wants passes over the boiling point of water or condensing point of steam. So the first temperature difference will be 140C to 100C and the second temperature difference will be from 100C to 50C. Once again, you will have to convert each of these Celcius values to Kelvin by adding 273.
For the first equation, you will need to use the value of specific heat capacity of steam as steam is what is being condensed in the first part of the process. For the second equation, you will need to use the value of specific heat capacity of water because below 100C water is in liquid state and that is now being further cooled. Your third equation will consider latent heat of vapourisation because that is the energy required to cause the change in state. The mass of water is given as 68 kg. So just as you did in task 2, use these equations to total the amount of heat energy that needs to be removed to cool the water.

In the next question, your previous answer will substitute for energy in the power equation. The question mentions that 68 kg of water is extracted in one minute i.e. 60 seconds. Thus, 60 is the denominator- time. I'm sure you're aware that the SI unit of power is Watt.

For the last question in this task, the crucial point to understand is the temperature difference. We are now talking about the air instead of the water in the tower. This air is being blown to cool the water; this happens due to a heat transfer taking place from the water to the air. Since water is at a higher temperature, heat flows from it to the air. Now air itself has a certain capacity up to which it can absorb and store heat without rising in temperature and it is this capacity that is defined as its specific heat capacity. So this makes it clear that for this answer, your equation will use the value of specific heat capacity of dry air. The question states that the upper limit for temp is 50C. We also know that current air temp is 8C. Since there is no other cooling system mentioned, we can safely assume that 8C is therefore the lower limit for temp. Thus, the temp difference to be used in this equation will be 50C-8C= 42C. Don't forget to convert this to Kelvin!
Mass of air is the variable in the equation that you are required to find out so that leaves us with heat energy. This refers to the heat energy of the water= heat energy that must be transferred from water to air to cool the water= the heat energy that the air gains= the answer to the first part. Substitute all known values in the equation to get the answer. Watch out for units.

Finally moving on to task 1. The first thing you need to know and find out is the various forms of energy. The next thing to know is that the most common form of energy that gets wasted is heat energy.
1. Electrical energy converted to kinetic to move the hoist. Heat and sound is wasted because they are of no use here. Kinetic energy of hoist is transferred to potential energy of packing case by virtue of its change of position.
2. Chemical energy of petrol is converted to electrical by the generator. Heat is wasted. Electrical is transferred to light energy and again heat is wasted due to resistance in the electrical components.
3. I'm not too sure about this one: potential energy of the restrain to elastic potential energy when it is stretched. Heat is wasted.
4. Chemical of battery to electric to sound/light. Heat given off at every transfer.
5. Electrical to heat.
6. Chemical energy of coal converted to heat energy of water causing it to boil. The steam from that process is used to move turbines so that heat energy is converted to kinetic energy. Sound may be produced so it is wasted. The electromagnets connected to the turbines then convert the kinetic energy to electrical. Heat energy is wasted.

Just to recap:

Specific heat capacity is the energy required to raise the temperature of 1 kg of a substance by 1 degree Celcius.
Latent heat of fusion is the energy required to cause a change of state from solid to liquid without raising the temperature of the substance.
Latent heat of vapourisation is the energy required to cause a change of state from liquid to gas without raising the temperature of the substance.

Let me know if you have more specific doubts. Please try to redo these questions on your own when you have time to ensure you have understood the concept. Hope this helps
1
3 years ago
#5
Also, you might find it helpful to go through Energy and Solids, Liquids and Gases learning guides on http://www.bbc.co.uk/education/subjects/zpm6fg8
0
Thread starter 3 years ago
#6
(Original post by Nikita Verma)
You're most welcome, I'm glad I could help.

You're answers are absolutely correct. The second value appears high because we have converted all values to Joules instead of keeping them in kJ. If you divide by 1000 to convert it, it may not seem so high after all.

Sure, I'll help you. I'll explain the other tasks which will also help you answer task 4, Once again, I won't give you the working or answers directly because that will be of no help; you need to understand the concept so you can attempt any questions on this topic.

Okay so task 3 is somewhat a reverse of task 2. One thing to keep in mind is that heat energy, the amount or value of it remains the same- you can input a certain amount of heat energy to raise something by a certain temperature and you can remove the same amount of heat energy to cause the same reduction in temperature. This is why the formula remains the same irrespective of whether the mass in question is being heated or cooled. So we heated Zinc in task 2 and now we're cooling water in task 3. Same formulae.

Just like task 2, the temperature difference (from 140C to 50C) the question wants passes over the boiling point of water or condensing point of steam. So the first temperature difference will be 140C to 100C and the second temperature difference will be from 100C to 50C. Once again, you will have to convert each of these Celcius values to Kelvin by adding 273.
For the first equation, you will need to use the value of specific heat capacity of steam as steam is what is being condensed in the first part of the process. For the second equation, you will need to use the value of specific heat capacity of water because below 100C water is in liquid state and that is now being further cooled. Your third equation will consider latent heat of vapourisation because that is the energy required to cause the change in state. The mass of water is given as 68 kg. So just as you did in task 2, use these equations to total the amount of heat energy that needs to be removed to cool the water.

In the next question, your previous answer will substitute for energy in the power equation. The question mentions that 68 kg of water is extracted in one minute i.e. 60 seconds. Thus, 60 is the denominator- time. I'm sure you're aware that the SI unit of power is Watt.

For the last question in this task, the crucial point to understand is the temperature difference. We are now talking about the air instead of the water in the tower. This air is being blown to cool the water; this happens due to a heat transfer taking place from the water to the air. Since water is at a higher temperature, heat flows from it to the air. Now air itself has a certain capacity up to which it can absorb and store heat without rising in temperature and it is this capacity that is defined as its specific heat capacity. So this makes it clear that for this answer, your equation will use the value of specific heat capacity of dry air. The question states that the upper limit for temp is 50C. We also know that current air temp is 8C. Since there is no other cooling system mentioned, we can safely assume that 8C is therefore the lower limit for temp. Thus, the temp difference to be used in this equation will be 50C-8C= 42C. Don't forget to convert this to Kelvin!
Mass of air is the variable in the equation that you are required to find out so that leaves us with heat energy. This refers to the heat energy of the water= heat energy that must be transferred from water to air to cool the water= the heat energy that the air gains= the answer to the first part. Substitute all known values in the equation to get the answer. Watch out for units.

Finally moving on to task 1. The first thing you need to know and find out is the various forms of energy. The next thing to know is that the most common form of energy that gets wasted is heat energy.
1. Electrical energy converted to kinetic to move the hoist. Heat and sound is wasted because they are of no use here. Kinetic energy of hoist is transferred to potential energy of packing case by virtue of its change of position.
2. Chemical energy of petrol is converted to electrical by the generator. Heat is wasted. Electrical is transferred to light energy and again heat is wasted due to resistance in the electrical components.
3. I'm not too sure about this one: potential energy of the restrain to elastic potential energy when it is stretched. Heat is wasted.
4. Chemical of battery to electric to sound/light. Heat given off at every transfer.
5. Electrical to heat.
6. Chemical energy of coal converted to heat energy of water causing it to boil. The steam from that process is used to move turbines so that heat energy is converted to kinetic energy. Sound may be produced so it is wasted. The electromagnets connected to the turbines then convert the kinetic energy to electrical. Heat energy is wasted.

Just to recap:

Specific heat capacity is the energy required to raise the temperature of 1 kg of a substance by 1 degree Celcius.
Latent heat of fusion is the energy required to cause a change of state from solid to liquid without raising the temperature of the substance.
Latent heat of vapourisation is the energy required to cause a change of state from liquid to gas without raising the temperature of the substance.

Let me know if you have more specific doubts. Please try to redo these questions on your own when you have time to ensure you have understood the concept. Hope this helps

Thanks soo much!! You are actually probably the MOST helpful person I've come across you know!! I've actually started to understand this better as well!

I've got a bit of questions for these tasks:

You know how for the seat belt one; isn't the first energy kinetic energy of the seat belt/driver and then the rest that you said, but with kinetic energy of the seat belt again at the last part? Also, at which part does heat energy (as wasted energy) come into the flow chart - is that heat energy at the potential energy and elastic energy part?

Are these the right answers for each of the questions:

1)
6786400J from 150C to 100C
154360000J from the condensation part
14235800J from 100C to 50C
And then the total, which is 175382200J
2)
2923036.67W
3)
4150.86kg
Also, I got one question: Why do you transfer to kelvin when the temperature difference will still be the same as when you keep it as degrees celcius? And why does it mention the specific heat capacity of ice in the question, when it doesn't really need to be used? Is that just to confuse you or something?

Is this all correct for this question:

- Explain how it works
The steam comes into the cooling tower at 140C and it is then cooled by the cool atmospheric air being blown over the pipes that have the steam inside.

It then cools to water at a temperature of 50C as a result of this cool atmospheric air being blown in and then exits the tower.

At the base of the cooling tower, a powerful fan is present, which allows the air to be forced through the tower.

- Explain the process by which the energy in the steam is reduced so that it becomes a liquid at a lower temperature
The amount of heat energy remains the same; a certain amount of heat energy can be inputted to raise something by a certain temperature and the same amount of energy can also be removed in order to cause the same reduction in temperature. In the case of the cooling tower, the heat energy within the steam was removed in order for it to become a liquid at a lower temperature.

The temperature difference (150C to 50C) passes over the boiling point of water or the condensing point of steam. The first temperature difference of this process is from 140C to 100C and the second temperature difference is from 100C to 50C.

Steam is what is being condensed in the first part of the process which is why the specific heat capacity of steam was used in the first equation. The next equation was the latent heat of vapouration as this is the energy that is needed in order to cause the change in state, from steam to liquid. In the next equation, the specific heat capacity of water was used as below 100C, the water is in liquid state (that is being further cooled to 50C).

- Explain the process by which the air stores the energy absorbed from the water
The air is used in the cooling tower to cool the water. This cooling in the water happens because of heat transfer taking place from the water to the air.

Due to the water being at a higher temperature than the air, heat flows from it to the air.

Air itself has a certain capacity up to which it is able to absorb and store heat without rising in temperature and it is this capacity that is defined as the specific heat capacity, which why the specific heat capacity of dry air was used in the question earlier.

The temperature is 50C for the upper limit and the current air temperature is 8C and due to there being no other cooling system mentioned in the question, it can be assumed that 8C is the lower limit for temperature, therefore the temperature difference to be used in the question was 42C (50C - 8C).
0
Thread starter 3 years ago
#7
(Original post by Nikita Verma)
Also, you might find it helpful to go through Energy and Solids, Liquids and Gases learning guides on http://www.bbc.co.uk/education/subjects/zpm6fg8
Yee, I'll definitely be going through that!
0
3 years ago
#8
Once again, you're welcome, I'm just happy to have been of help to you.

Task 1: You do have a point that the initial energy should be kinetic as the car and by extension the seat belt was moving. However, the reason I feel it is not relevant here is because we need to consider the frame of reference. For someone standing outside the car, they see the car and everything inside it moving because they are stationary. But for a person inside the car, the car and all its components are moving at the same speed. So imagine you're sitting in a car and the windows are opaque- there is no way you can look outside. If you could feel no motion- no wheels turning, no engine revving up, no bumps in the road, no force pushing you in your seat as the car accelerates- then how can you tell that the car is moving? Everything in the car is moving along with you at the same velocity so you have nothing else to compare it to so for all you know, you could actually be in a stationary car. So back to your question, the seat belt is in motion but so is everything else in the car including the seat, the seat belt holder and the person the seat belt is holding back. Furthermore, during a collision, it is not the car's kinetic energy that is transferred to the seat belt- the seat belt was already stretched so it had potential energy by virtue of its arrangement. The car's kinetic energy gets converted to heat and sound on colliding. At least this is what I think is right, you might want to confirm this from your teacher. As for where does heat energy come in, if you're drawing an arrow from potential to elastic potential in your flowchart, you'll have to show another arrow pointing away from this arrow to represent wasted energy. Heat energy in this case arises due to friction within and around the seat belt upon it being stretched to hold back the person.

Task 3: I'm afraid you made a silly error in calculating the first part: the temp difference is from 140C to 100C not from 150C. Be careful! I used to make a lot of such careless errors in a hurry during calculations until they were the only marks I was losing on an exam so I made a conscious effort to read and re-read the question where values were mentioned Also the third calculation, I'm getting the answer as 91,963,268 J (68 x 4187 x 323) so just have a look at that again. This will change your total and therefore the rest of the answers for this task.

Answer: You're right, the temp difference remains the same but the value is different i.e. 50C - 40C = 10C and 323 K - 313 K = 10 K. BUT 10 C does not equal 10 K but instead is 283 K. And this value is the one we need for the equation. We convert to Kelvin because if you look at the units of specific heat capacity, it is given in SI units and there is per Kelvin and not per degree Celcius. For any equation to be correct, the units of the quantities on the right hand side must be equal to the units of the quantities on the left hand side. For e.g. power= energy/time. Power is measured in Watts which is also written as Joules/second. How do we know this equation is correct and that it should not be energy x time instead? Because Energy is measured in Joules and time in seconds so when we divide them, we get Joules/second which is equal to Watts.

Task 4: It's not entirely correct because a lot of it is copied from my explanation and I did not use scientific terms when trying to simplify it for you so everything looks out of order when you try to fit it in to answer this question. Take a day or two (You have time till Monday and I'm online daily to help so take your time but do it thoroughly once and for all) , read through the learning guides in the link above and re-attempt this question in your own words. Then if it's still not right, I'll explain it to you and help you frame the answer. I'm sorry but doing it yourself is the only way you'll really understand and learn the topic.
When reading the guides, pay close attention to the ones on heat and temperature because they will introduce you to a slightly new concept which will help you correctly answer "Explain the process by which the air stores the energy absorbed from the water".
0
3 years ago
#9
"And why does it mention the specific heat capacity of ice in the question, when it doesn't really need to be used? Is that just to confuse you or something?"

Yes, it is of no use and is merely there to confuse and distract you. It is test of the student's confidence in their knowledge Get used to selecting useful data from that which is provided, exam questions almost always have extra information.
0
Thread starter 3 years ago
#10
(Original post by Nikita Verma)
Once again, you're welcome, I'm just happy to have been of help to you.

Task 1: You do have a point that the initial energy should be kinetic as the car and by extension the seat belt was moving. However, the reason I feel it is not relevant here is because we need to consider the frame of reference. For someone standing outside the car, they see the car and everything inside it moving because they are stationary. But for a person inside the car, the car and all its components are moving at the same speed. So imagine you're sitting in a car and the windows are opaque- there is no way you can look outside. If you could feel no motion- no wheels turning, no engine revving up, no bumps in the road, no force pushing you in your seat as the car accelerates- then how can you tell that the car is moving? Everything in the car is moving along with you at the same velocity so you have nothing else to compare it to so for all you know, you could actually be in a stationary car. So back to your question, the seat belt is in motion but so is everything else in the car including the seat, the seat belt holder and the person the seat belt is holding back. Furthermore, during a collision, it is not the car's kinetic energy that is transferred to the seat belt- the seat belt was already stretched so it had potential energy by virtue of its arrangement. The car's kinetic energy gets converted to heat and sound on colliding. At least this is what I think is right, you might want to confirm this from your teacher. As for where does heat energy come in, if you're drawing an arrow from potential to elastic potential in your flowchart, you'll have to show another arrow pointing away from this arrow to represent wasted energy. Heat energy in this case arises due to friction within and around the seat belt upon it being stretched to hold back the person.

Task 3: I'm afraid you made a silly error in calculating the first part: the temp difference is from 140C to 100C not from 150C. Be careful! I used to make a lot of such careless errors in a hurry during calculations until they were the only marks I was losing on an exam so I made a conscious effort to read and re-read the question where values were mentioned Also the third calculation, I'm getting the answer as 91,963,268 J (68 x 4187 x 323) so just have a look at that again. This will change your total and therefore the rest of the answers for this task.

Answer: You're right, the temp difference remains the same but the value is different i.e. 50C - 40C = 10C and 323 K - 313 K = 10 K. BUT 10 C does not equal 10 K but instead is 283 K. And this value is the one we need for the equation. We convert to Kelvin because if you look at the units of specific heat capacity, it is given in SI units and there is per Kelvin and not per degree Celcius. For any equation to be correct, the units of the quantities on the right hand side must be equal to the units of the quantities on the left hand side. For e.g. power= energy/time. Power is measured in Watts which is also written as Joules/second. How do we know this equation is correct and that it should not be energy x time instead? Because Energy is measured in Joules and time in seconds so when we divide them, we get Joules/second which is equal to Watts.

Task 4: It's not entirely correct because a lot of it is copied from my explanation and I did not use scientific terms when trying to simplify it for you so everything looks out of order when you try to fit it in to answer this question. Take a day or two (You have time till Monday and I'm online daily to help so take your time but do it thoroughly once and for all) , read through the learning guides in the link above and re-attempt this question in your own words. Then if it's still not right, I'll explain it to you and help you frame the answer. I'm sorry but doing it yourself is the only way you'll really understand and learn the topic.
When reading the guides, pay close attention to the ones on heat and temperature because they will introduce you to a slightly new concept which will help you correctly answer "Explain the process by which the air stores the energy absorbed from the water".

Thanks soo much again!

I do kind of get it a bit more now, so would it be kinetic energy topotential energy of the restraint, then an arrow underneath to represent the wasted heat energy then elastic potential energy?

Are these the right answers now:

1)
5429120J
154360000J
14235800J
Total - 174024920J

2)
2900415.33W

3)
4118.74kg (as wouldn't it be 174024920J / 1.006kJKGK x 42K due to the equation being M = E / CT as isn't the mass being worked out?).

That makes much more sense on why we use kelvin now, so thanks soo much

Is the part where it says 'explain how it works' and 'explain the process by which the energy in the steam is reduced so that it becomes a liquid at a lower temperature' correct for this and it's just the part where it says ' explain the process by which the air stores the energy absorbed from the water' that needs to be corrected?
0
Thread starter 3 years ago
#11
(Original post by Nikita Verma)
"And why does it mention the specific heat capacity of ice in the question, when it doesn't really need to be used? Is that just to confuse you or something?"

Yes, it is of no use and is merely there to confuse and distract you. It is test of the student's confidence in their knowledge Get used to selecting useful data from that which is provided, exam questions almost always have extra information.
Haha, yee I did think so!
0
3 years ago
#12

(Original post by Ak786454)
Thanks soo much again!

I do kind of get it a bit more now, so would it be kinetic energy topotential energy of the restraint, then an arrow underneath to represent the wasted heat energy then elastic potential energy?

Are these the right answers now:

1)
5429120J
154360000J
14235800J
Total - 174024920J

2)
2900415.33W

3)
4118.74kg (as wouldn't it be 174024920J / 1.006kJKGK x 42K due to the equation being M = E / CT as isn't the mass being worked out?).

That makes much more sense on why we use kelvin now, so thanks soo much

Is the part where it says 'explain how it works' and 'explain the process by which the energy in the steam is reduced so that it becomes a liquid at a lower temperature' correct for this and it's just the part where it says ' explain the process by which the air stores the energy absorbed from the water' that needs to be corrected?
Task 1: The seat belt can initially have either potential energy or kinetic energy, I don't think it would be wise to put in both. So do ask your teacher for feedback on this.

Task 3: I'm afraid our answers for the first part don't match again. Perhaps I'm making a mistake. I've attached an image of my calculations, you can compare them to your working and check where they differ.

Task 4: 'Explain how it works' is okay but it seems too similar to the information in the question. Perhaps you could add in a bit about the cooling fan being placed at the bottom of the tower to use convection currents as part of the cooling mechanism as portrayed by the arrows in the diagram. You could then go on to explain how the current is set up. I'm afraid 'explain the process by which the energy in the steam is reduced so that it becomes a liquid at a lower temperature' while being correct in essentials, does not use scientific terms so it is a vague answer and therefore not entirely correct. It does not include energy at a molecular level nor does it mention latent heat. It will be easier to answer once you've read the learning guides.
0
Thread starter 3 years ago
#13
(Original post by Nikita Verma)

Task 1: The seat belt can initially have either potential energy or kinetic energy, I don't think it would be wise to put in both. So do ask your teacher for feedback on this.

Task 3: I'm afraid our answers for the first part don't match again. Perhaps I'm making a mistake. I've attached an image of my calculations, you can compare them to your working and check where they differ.

Task 4: 'Explain how it works' is okay but it seems too similar to the information in the question. Perhaps you could add in a bit about the cooling fan being placed at the bottom of the tower to use convection currents as part of the cooling mechanism as portrayed by the arrows in the diagram. You could then go on to explain how the current is set up. I'm afraid 'explain the process by which the energy in the steam is reduced so that it becomes a liquid at a lower temperature' while being correct in essentials, does not use scientific terms so it is a vague answer and therefore not entirely correct. It does not include energy at a molecular level nor does it mention latent heat. It will be easier to answer once you've read the learning guides.
Okay, I'll ask my teacher for that one for task 1 in that case

I think I see what is different now; I worked out the change in temperature, as aren't I supposed to do that? I done that in task 2 for zinc as well.

E.g. I done this for the 140C to 100C:
From 140C to 100C
140C = 413K
100C = 373K

Eq = MC(delta)T
= 68kg x 1996 Jkgk x (413 - 373)K
= 5429120J

I'll have a try at doing that then - I've started reading them and I should be able to finish it today later.
0
3 years ago
#14
(Original post by Ak786454)
Okay, I'll ask my teacher for that one for task 1 in that case

I think I see what is different now; I worked out the change in temperature, as aren't I supposed to do that? I done that in task 2 for zinc as well.

E.g. I done this for the 140C to 100C:
From 140C to 100C
140C = 413K
100C = 373K

Eq = MC(delta)T
= 68kg x 1996 Jkgk x (413 - 373)K
= 5429120J

I'll have a try at doing that then - I've started reading them and I should be able to finish it today later.
Ah, this was my turn to make a careless mistake. I'm so sorry. Your calculations are correct. I made a mistake while calculating delta T. So your answers for the rest of the question are correct too.
I think I've learnt my lesson- no shortcuts.

That's great. Let me know if you need help. Don't hesitate to PM me with any other doubts in physics or another subject.
0
Thread starter 3 years ago
#15
(Original post by Nikita Verma)
Ah, this was my turn to make a careless mistake. I'm so sorry. Your calculations are correct. I made a mistake while calculating delta T. So your answers for the rest of the question are correct too.
I think I've learnt my lesson- no shortcuts.

That's great. Let me know if you need help. Don't hesitate to PM me with any other doubts in physics or another subject.
Oh that's okay then I was about to start getting really confused then!! At least task 3 is now finished.

And with task 4, I did try reading the website you gave me but I don't get how to include it within this task Is there any possibility of you helping me on it?
0
3 years ago
#16
(Original post by Ak786454)
And with task 4, I did try reading the website you gave me but I don't get how to include it within this task Is there any possibility of you helping me on it?
- Explain how it works
The steam comes into the cooling tower at 140C and it is then cooled by the cool atmospheric air being blown over the pipes that have the steam inside.

It then cools to water at a temperature of 50C as a result of this cool atmospheric air being blown in and then exits the tower.

At the base of the cooling tower, a powerful fan is present, which allows the air to be forced through the tower.

Thermal energy is transferred from the hot pipes to the cool air by conduction and convection.
Refer (http://www.edinformatics.com/math_sc...ransferred.htm )

- Explain the process by which the energy in the steam is reduced so that it becomes a liquid at a lower temperature

The highly energetic steam molecules collide with the inner walls of the pipe and through this direct contact, thermal energy is transferred to the cooler pipe walls by conduction. Similarly, thermal energy is then transferred to the cool air being forced through the tower. As the air heats up, it rises and transfers the heat to other air molecules by convection. This flow of thermal energy from the steam molecules to air molecules causes the steam molecules to lose energy and thus become cooler. As more cool air is continuously blown in, steam molecules lose sufficient energy to condense to form liquid water. Their molecules have a lower energy now and thus cannot escape the intermolecular forces which bring them closer to cause a change of state from gas to liquid.
To help you complete this answer, here are some pointers on the physics of heat & temp but you're going to have to understand and tailor the concept to fit this question:

1. The internal energy of a system is the sum of the random distribution of kinetic and potential energies of its atoms and molecules.
2. Temperature is the average internal energy of a system.
3. Increase in kinetic energy leads to an increase in temperature. Increase in potential energy does increase the internal energy but does not cause a change in temperature- this is defined as latent heat.
4. Energy flowing from a region of higher temp to a region of lower temp is called thermal energy.
5. When 2 objects, in contact with each other, are at the same temp, there will be no transfer of thermal energy between them and they are said to be in a state of thermal equilibrium.
- Explain the process by which the air stores the energy absorbed from the water

Air molecules heat up i.e. they become energised and gain kinetic energy. So warm air rises to the top of the tower. Here, in the absence of hot pipes, the air molecules lose energy as they collide with each other and the inner walls of the tower. Thus the air becomes cooler. Cold air is heavier and so it descends to where the hot pipes are, only to heat up again and this way a convection current is set up which allows air to continuously absorb, store and lose heat energy.

The underlined sentences above are a slightly higher level explanation. I wasn't sure which grade you're studying at so I put in that extra info too. Looking at the questions I would guess GCSE level or lower. The underlined sentences contain text from A Level physics. So unless you're studying A2 Physics, you don't need to go into such depth.
0
Thread starter 3 years ago
#17
(Original post by Nikita Verma)
- Explain how it works
The steam comes into the cooling tower at 140C and it is then cooled by the cool atmospheric air being blown over the pipes that have the steam inside.

It then cools to water at a temperature of 50C as a result of this cool atmospheric air being blown in and then exits the tower.

At the base of the cooling tower, a powerful fan is present, which allows the air to be forced through the tower.

Thermal energy is transferred from the hot pipes to the cool air by conduction and convection.
Refer (http://www.edinformatics.com/math_sc...ransferred.htm )

- Explain the process by which the energy in the steam is reduced so that it becomes a liquid at a lower temperature

The highly energetic steam molecules collide with the inner walls of the pipe and through this direct contact, thermal energy is transferred to the cooler pipe walls by conduction. Similarly, thermal energy is then transferred to the cool air being forced through the tower. As the air heats up, it rises and transfers the heat to other air molecules by convection. This flow of thermal energy from the steam molecules to air molecules causes the steam molecules to lose energy and thus become cooler. As more cool air is continuously blown in, steam molecules lose sufficient energy to condense to form liquid water. Their molecules have a lower energy now and thus cannot escape the intermolecular forces which bring them closer to cause a change of state from gas to liquid.
To help you complete this answer, here are some pointers on the physics of heat & temp but you're going to have to understand and tailor the concept to fit this question:

1. The internal energy of a system is the sum of the random distribution of kinetic and potential energies of its atoms and molecules.
2. Temperature is the average internal energy of a system.
3. Increase in kinetic energy leads to an increase in temperature. Increase in potential energy does increase the internal energy but does not cause a change in temperature- this is defined as latent heat.
4. Energy flowing from a region of higher temp to a region of lower temp is called thermal energy.
5. When 2 objects, in contact with each other, are at the same temp, there will be no transfer of thermal energy between them and they are said to be in a state of thermal equilibrium.
- Explain the process by which the air stores the energy absorbed from the water

Air molecules heat up i.e. they become energised and gain kinetic energy. So warm air rises to the top of the tower. Here, in the absence of hot pipes, the air molecules lose energy as they collide with each other and the inner walls of the tower. Thus the air becomes cooler. Cold air is heavier and so it descends to where the hot pipes are, only to heat up again and this way a convection current is set up which allows air to continuously absorb, store and lose heat energy.

The underlined sentences above are a slightly higher level explanation. I wasn't sure which grade you're studying at so I put in that extra info too. Looking at the questions I would guess GCSE level or lower. The underlined sentences contain text from A Level physics. So unless you're studying A2 Physics, you don't need to go into such depth.
Thanks so much for your help!! I'm studying ALevel Physics btw and we just had to do this as our teacher said it'll help us a lot with the practical work we have to do in class and the written work that needs to be produced with it as we can use some of the information in it.

Also, you know how it says to use the words, specific heat and latent heat with this task, where can I use those in this task?
0
3 years ago
#18
(Original post by Ak786454)
Thanks so much for your help!! I'm studying ALevel Physics btw and we just had to do this as our teacher said it'll help us a lot with the practical work we have to do in class and the written work that needs to be produced with it as we can use some of the information in it.

Also, you know how it says to use the words, specific heat and latent heat with this task, where can I use those in this task?
You're welcome

Oh, I see. Which board are you studying?

Latent heat will be included in the answer about steam changing into water because there is a change of state there. I have mentioned latent heat in the extra pointers so you can include that in your answer.

Specific heat capacity will be included when explaining how air stores the heat. You can compare the values of s.h.c. of dry air, steam and water. The higher the value, the more capacity the substance has to store heat i.e. the longer (or more heat energy) it will take to raise its temp.
0
Thread starter 3 years ago
#19
(Original post by Nikita Verma)
You're welcome

Oh, I see. Which board are you studying?

Latent heat will be included in the answer about steam changing into water because there is a change of state there. I have mentioned latent heat in the extra pointers so you can include that in your answer.

Specific heat capacity will be included when explaining how air stores the heat. You can compare the values of s.h.c. of dry air, steam and water. The higher the value, the more capacity the substance has to store heat i.e. the longer (or more heat energy) it will take to raise its temp.
I'm studying Edexcel Physics. What do you study - are you at university?

For the specific heat capacity: Should I just say, in another paragraph ‘The dry air has less capacity (in comparison with the water and steam) to store heat, which means it’ll take less time (or less heat energy) in order for it to raise its temperature, so it's ideal for the process for it to store heat energy from water to cool it to liquid water'.

I tried to include latent heat in my answer but don't understand where.
It's really confusing :/
0
3 years ago
#20
(Original post by Ak786454)
I'm studying Edexcel Physics. What do you study - are you at university?

For the specific heat capacity: Should I just say, in another paragraph ‘The dry air has less capacity (in comparison with the water and steam) to store heat, which means it’ll take less time (or less heat energy) in order for it to raise its temperature, so it's ideal for the process for it to store heat energy from water to cool it to liquid water'.

I tried to include latent heat in my answer but don't understand where.
It's really confusing :/
No worries

- Explain the process by which the energy in the steam is reduced so that it becomes a liquid at a lower temperature

The highly energetic steam molecules collide with the inner walls of the pipe and through this direct contact, thermal energy is transferred to the cooler pipe walls by conduction. Similarly, thermal energy is then transferred to the cool air being forced through the tower. As the air heats up, it rises and transfers the heat to other air molecules by convection. This flow of thermal energy from the steam molecules to air molecules causes the steam molecules to lose kinetic energy and thus become cooler. As more cool air is continuously blown in, steam molecules lose sufficient energy to condense to form liquid water. Their molecules have a lower potential energy now and thus cannot escape the intermolecular forces which bring them closer to cause a change of state from gas to liquid. This process of change in state occurs at 100C (condensation point of steam) where the temperature stabilises for a while but heat energy is being continuously lost to the cool air. This is the specific latent heat of water where the potential energy of the molecules changes but kinetic remains the same causing no change in temp but a change of state instead. Once the energy required for the change of state has been lost, the temp of water reduces again as more cool air is blown into the tower.

Also, your paragraph on dry air is really good. You've hit the bull's eye on interpreting why dry air is used based on s.h.c. You can also mention that it's ideal also because it takes up lesser time, since air is a very mobile fluid it can be easily pumped around and the ease of a natural convection current being set up aids the efficiency of the cooling of steam.

I'm on a gap year. I sat my CIE A Levels last year. I studied the 3 sciences, Psychology and English so if you have questions in any of these other subjects, feel free to PM me.

Here's another website I found helpful to study from: http://www.s-cool.co.uk/a-level/phys...mal-properties

Hope this helps
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