# M2 Energy Question

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#1
In this video

http://www.examsolutions.net/maths-r...tutorial-1.php

an answer of +130J is obtained. However when I use the formula from question 2 in this booklet,

I get an answer of -130J. Is there a meaning behind the negative or have I done something wrong?

Thanks
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#2
Here is my working -
0
4 years ago
#3
Without watching the videos, I would probably say either a you did a mistake with a minus sign or it might depend if you were working upwards or downwards maybe? There is also the possibility exam solutions is wrong
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#4
Thanks for the reply! I've repeated the question from the first link multiple times now and I still seem to be getting the negative version of the examsolutions answer, and using the same formula for Q2 in the second link, I get the correct answer of 8920J
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4 years ago
#5
Hmm, exam solutions could be wrong
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4 years ago
#6
(Original post by PhyM23)
In this video

http://www.examsolutions.net/maths-r...tutorial-1.php

an answer of +130J is obtained. However when I use the formula from question 2 in this booklet,

I get an answer of -130J. Is there a meaning behind the negative or have I done something wrong?

Thanks
(Original post by PhyM23)
Here is my working -
I do no have time to watch the video but following the question from the info in your working I also get -130.

this means that the cyclist is not putting energy into the system, but took some energy out... (physical explanation he applied the brakes)
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#7
(Original post by TeeEm)
I do no have time to watch the video but following the question from the info in your working I also get -130.

this means that the cyclist is not putting energy into the system, but took some energy out... (physical explanation he applied the brakes)
Thanks for the reply! I don't quite understand why braking would take energy out of the system? In to which form is it transferred?
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4 years ago
#8
(Original post by PhyM23)
Thanks for the reply! I don't quite understand why braking would take energy out of the system? In to which form is it transferred?
You have a balance sheet in mechanical energy (KE and PE)

energy can come in
cyclist pedalling, or a battery assisted bike

energy can be moved out
air resistance, braking
1
#9
(Original post by TeeEm)
You have a balance sheet in mechanical energy (KE and PE)

energy can come in
cyclist pedalling, or a battery assisted bike

energy can be moved out
air resistance, braking
Ah that makes sense now. Thanks very much!
0
4 years ago
#10
(Original post by PhyM23)
In this video

http://www.examsolutions.net/maths-r...tutorial-1.php

an answer of +130J is obtained. However when I use the formula from question 2 in this booklet,

I get an answer of -130J. Is there a meaning behind the negative or have I done something wrong?

Thanks
Well thats quite the brain teaser
0
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