Sqa higher physics

I struggle with the theory and explaining questions a lot. We're in the same boat my friend, i do textbook questions and they're all fine but one past paper question and I'm done

Reply 2

gwagon

18

I was in the same boat as you last year, when I did Higher Physics(HP).
From Old Higher, the explain questions where quite formulaic. They would usually be preceded by a calculation. My teacher said that usually, they change a variable and YOU are expected to use the equation from before to explain what happens when the variable changes.
E.g.
Q1.a. Car A is 800kgs and is accelerating at 2ms^-2. Calculate its force. (f = ma, F = 800 * 2 = 1600N)
Q1.b. Car A is replaced by Car B, which has a higher mass than Car A, and has the same acceleration. Explain what would happen to the magnitude of Car B's force.
Now you can use the same equation from 1.a.(f = ma) and apply logic. In your answer, you'd mention how a(acceleration) would be constant, but m(mass) is bigger, hence the force from Car B would be bigger.
Always explain what the steps you take to arrive to your answer in an 'explain' type question very thoroughly.

Obviously, this is an over-simplification of the process, but this is roughly what you would do - at least that's what I did for Old Higher.
For pulley problems, or any problem involving forces, I would STRONGLY suggest you draw a free body diagram and individually resolve vertical and horizontal components to find your desired force.

If you have further problems, I would recommend YouTube as a source for study material. There are a TON of videos on physics, many of which cover more than what you need to know. Khan Academy and Bozeman Science are some good examples.

Reply 3

Science_Girl

12

Free body diagrams for anything to do with forces. Just helps to visualise what is going on.
For explanations my teacher always says to write out formulae and which variables are directly proportional to which then write linking statements and conclusion at the end

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Reply 4

Where about is everyone in the course? What topics have you covered?

Reply 5

Science_Girl

12

We have done the second part of Particles & Waves and the whole of Our Dynamic Universe. This sounds like a weird order, but apparently this means we build on our knowledge continuously. We also have just started our assignments. Not looking forward to electricity though :/

Reply 6

Can someone please help with this question. I know the method for working it out but for some reason I get none of the above answers!!! PLEASE HELP! Run the numbers through and you should see what I mean. Btw the correct answer is C (12J) how to get this!?!?!??!?!

momentum question tsr.png

Reply 7

Original post by Science_Girl

We have done the second part of Particles & Waves and the whole of Our Dynamic Universe. This sounds like a weird order, but apparently this means we build on our knowledge continuously. We also have just started our assignments. Not looking forward to electricity though :/

You are way ahead of us! How is the second part of Our dynamic universe? I have only done up to special relativity so curious about the rest! Have you started the first half of particles and waves??? Yeah we are really far behind but how is the theory of ODU part 2? Apparently there is a lot to learn???

Reply 8

Original post by Jeff548

Can someone please help with this question. I know the method for working it out but for some reason I get none of the above answers!!! PLEASE HELP! Run the numbers through and you should see what I mean. Btw the correct answer is C (12J) how to get this!?!?!??!?!

momentum question tsr.png

This is a common exam question. I will show you the way I tackle these questions.

Momentum Before collision=Momentum After Collison
(6x1) + (2x0) = (3 x v) three is the combined mass.
6 = 3v
v = 2m/s to the right.

Now we can tackle the energy side of this problem. The energy before the collison was 0.5mv2 so (0.5 x 1 x 6^2) = 18J. The energy after the collison was (0.5 x 3 x 2^2) = 6J. This means that the energy lost was 18J - 6J = 12J. Hope that helps!

Reply 9

Original post by Jeff548

You are way ahead of us! How is the second part of Our dynamic universe? I have only done up to special relativity so curious about the rest! Have you started the first half of particles and waves??? Yeah we are really far behind but how is the theory of ODU part 2? Apparently there is a lot to learn???

We've also done all of ODU and half of Particles and Waves. After special relativity, you'll be pleased to hear that its fairly straightforward, well for me anyway. You learn about Doppler Redshift and Doppler Effect which is simple! Then you learn about the evidence for the expanding universe. Particle and Waves does have more theory to remember such as the Standard model and particle accelerators. Slightly foreign first but really easy to remember! Don't worry. Every class has a different speed. As long as you get the course finished lol :smile:

Reply 10

Original post by Zahrah1234

This is a common exam question. I will show you the way I tackle these questions.

Momentum Before collision=Momentum After Collison
(6x1) + (2x0) = (3 x v) three is the combined mass.
6 = 3v
v = 2m/s to the right.

Now we can tackle the energy side of this problem. The energy before the collison was 0.5mv2 so (0.5 x 1 x 6^2) = 18J. The energy after the collison was (0.5 x 3 x 2^2) = 6J. This means that the energy lost was 18J - 6J = 12J. Hope that helps!

Thanks for that but I am still confused. If they stick together, then why would you work out the velocity because the final velocity should just be the same for both carts shouldn't it???? And since trolley 1 is moving at 6m/s then both trolleys should be moving at 6m/s after the collision since they join together????

Reply 11

Original post by Zahrah1234

We've also done all of ODU and half of Particles and Waves. After special relativity, you'll be pleased to hear that its fairly straightforward, well for me anyway. You learn about Doppler Redshift and Doppler Effect which is simple! Then you learn about the evidence for the expanding universe. Particle and Waves does have more theory to remember such as the Standard model and particle accelerators. Slightly foreign first but really easy to remember! Don't worry. Every class has a different speed. As long as you get the course finished lol :smile:

Yeah was just really worried because we have only done half of ODU and half of particles and waves but have our prelim in nearly a 3 weeks so no idea how we will finish in time!?!??

Reply 12

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Original post by Jeff548

Thanks for that but I am still confused. If they stick together, then why would you work out the velocity because the final velocity should just be the same for both carts shouldn't it???? And since trolley 1 is moving at 6m/s then both trolleys should be moving at 6m/s after the collision since they join together????

I always thought of it like this: Say you were running into a person at 6m/s. That person would be in your way, so you would slow down and would not continue at 6m/s. This is why you have to calculate the speed after the collison because energy is lost. I hope you understand! But if you don't I'll try my best again to answer lol :smile:

Reply 13

Original post by Jeff548

Yeah was just really worried because we have only done half of ODU and half of particles and waves but have our prelim in nearly a 3 weeks so no idea how we will finish in time!?!??

Haha, fret not. You're teachers know best. My prelim is also in three weeks now that I think of it lol. There is another class in my school who have two teachers and learn two units simultaneously. You would obviously not sit the prelim if you couldn't answer the questions. So don't worry! :smile:

Reply 14

Original post by Zahrah1234

I

I always thought of it like this: Say you were running into a person at 6m/s. That person would be in your way, so you would slow down and would not continue at 6m/s. This is why you have to calculate the speed after the collison because energy is lost. I hope you understand! But if you don't I'll try my best again to answer lol :smile:

Hey,
But i just looked in my CfE Higher Physics How to Pass book and it says:
how to pass.png

Reply 15

Original post by Jeff548

Hey,
But i just looked in my CfE Higher Physics How to Pass book and it says:
how to pass.png

I think the book is saying the right thing but is not clear about it. In class, we learned it as... the velocity after the collision is the same for both vehicles but is different from before the collision. If both vehicles are stuck together, their masses are combined (because they are moving as one), so they have the same velocity, BUT this velocity is different from before the collision, as energy is lost.

Reply 16

Original post by Zahrah1234

I think the book is saying the right thing but is not clear about it. In class, we learned it as... the velocity after the collision is the same for both vehicles but is different from before the collision. If both vehicles are stuck together, their masses are combined (because they are moving as one), so they have the same velocity, BUT this velocity is different from before the collision, as energy is lost.

The book says that you do not know the velocity after the collision. This means that you would have to work it out, and this is made easier knowing that the velocity of both the vehicles are the same, meaning you consider them as one.

Reply 17