# Work energy power

Watch
Announcements

Page 1 of 1

Go to first unread

Skip to page:

Question 5 - I Have tried this, but failed, I used MGH = 50 x 10 X 0.35 and found Heat energy is 120 KJ to its 120000 J, since power = output/input X 100%

I used that but my answer did not match. The ans is 15% but how? please show me the steps, Thank you

Question 6 - I have no clue.

0

reply

Report

#2

(Original post by

Question 5 - I Have tried this, but failed, I used MGH = 50 x 10 X 0.35 and found Heat energy is 120 KJ to its 120000 J, since power = output/input X 100%

I used that but my answer did not match. The ans is 15% but how? please show me the steps, Thank you

Question 6 - I have no clue.

**Gartley222**)Question 5 - I Have tried this, but failed, I used MGH = 50 x 10 X 0.35 and found Heat energy is 120 KJ to its 120000 J, since power = output/input X 100%

I used that but my answer did not match. The ans is 15% but how? please show me the steps, Thank you

Question 6 - I have no clue.

Fridges are insulated boxes that use a motor to drive a heat pump. the heat pump moves heat from the inside of the box to the outside of the box... but it doesn't remove the heat from the room in any way. The motor is also less than 100% efficient and will produce some heat while it is running.

0

reply

Report

#3

mgh so 50 x 10 x 0.35 = 175j so you got that right.

She does it 30 times per minute and question says 4 minutes. So 175j x 30 x 4 = 21000j. This is the useful energy

The total energy is the useful energy + energy wasted which is 120000j so add that to 21000j = 141000

So then useful output divide total input so 21000 divide 141000 x100 to get 14.89 percent = 15percent

She does it 30 times per minute and question says 4 minutes. So 175j x 30 x 4 = 21000j. This is the useful energy

The total energy is the useful energy + energy wasted which is 120000j so add that to 21000j = 141000

So then useful output divide total input so 21000 divide 141000 x100 to get 14.89 percent = 15percent

0

reply

(Original post by

mgh so 50 x 10 x 0.35 = 175j so you got that right.

She does it 30 times per minute and question says 4 minutes. So 175j x 30 x 4 = 21000j. This is the useful energy

The total energy is the useful energy + energy wasted which is 120000j so add that to 21000j = 141000

So then useful output divide total input so 21000 divide 141000 x100 to get 14.89 percent = 15percent

**Chocolate...s**)mgh so 50 x 10 x 0.35 = 175j so you got that right.

She does it 30 times per minute and question says 4 minutes. So 175j x 30 x 4 = 21000j. This is the useful energy

The total energy is the useful energy + energy wasted which is 120000j so add that to 21000j = 141000

So then useful output divide total input so 21000 divide 141000 x100 to get 14.89 percent = 15percent

Any thoughts about the question 6?

0

reply

Report

#5

(Original post by

Thank you very much! Now I am clear.

Any thoughts about the question 6?

**Gartley222**)Thank you very much! Now I am clear.

Any thoughts about the question 6?

1

reply

(Original post by

We havnt went into too much detail about the law of conservation energy yet in our gcse level only to knoe that energy cant be destroyed or created. Maybe take into account that when a fridge door is open, compressor still works at its optimum level and so room temperature is increased

**Chocolate...s**)We havnt went into too much detail about the law of conservation energy yet in our gcse level only to knoe that energy cant be destroyed or created. Maybe take into account that when a fridge door is open, compressor still works at its optimum level and so room temperature is increased

0

reply

(Original post by

You need to include the number of times the woman repeats the exercise... 4 minutes at 30 reps per minute as per the question.

Fridges are insulated boxes that use a motor to drive a heat pump. the heat pump moves heat from the inside of the box to the outside of the box... but it doesn't remove the heat from the room in any way. The motor is also less than 100% efficient and will produce some heat while it is running.

**Joinedup**)You need to include the number of times the woman repeats the exercise... 4 minutes at 30 reps per minute as per the question.

Fridges are insulated boxes that use a motor to drive a heat pump. the heat pump moves heat from the inside of the box to the outside of the box... but it doesn't remove the heat from the room in any way. The motor is also less than 100% efficient and will produce some heat while it is running.

0

reply

Report

#8

(Original post by

I have a question to you! how did you understand from the question that which one is output and which one is input? Any clues?

**Gartley222**)I have a question to you! how did you understand from the question that which one is output and which one is input? Any clues?

The question says that heat is generated from her legs muscles so we assume that this is the energy wasted. Input energy is the amount of energy supplied to a device so useful output energy + energy wasted = your total input

0

reply

(Original post by

i think you are talking about question 5 right as question 6 doesnt say anything about input or output.

The question says that heat is generated from her legs muscles so we assume that this is the energy wasted. Input energy is the amount of energy supplied to a device so useful output energy + energy wasted = your total input

**Chocolate...s**)i think you are talking about question 5 right as question 6 doesnt say anything about input or output.

The question says that heat is generated from her legs muscles so we assume that this is the energy wasted. Input energy is the amount of energy supplied to a device so useful output energy + energy wasted = your total input

0

reply

X

Page 1 of 1

Go to first unread

Skip to page:

### Quick Reply

Back

to top

to top