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Old Apr 28th 2017, 04:10 AM   #1
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Question Energy, work and power question

I can't work out why I'm getting the part ii wrong and I was wondering if you could help.

A mouse of mass 15g is stationary 2m below its hole. It runs to its hole, arriving 1.5 seconds later with a speed of 3ms^-1.

i) Show that the acceleration of the mouse it not constant. [Done by using s=ut+.5at^2 and v=u+at and showing that they give different answers for acceleration]

ii) Calculate the average power of the mouse

Since power = work done / time and work done = .5mv^2 - .5mu^2, power = ((0.5*0.015*3^2) - 0) / 1.5
=0.045W.

However, the book gives the answer 0.241W.
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Old Apr 28th 2017, 04:51 AM   #2
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Don't forget that the work done includes both the gain in KE and the gain in PE as the mouse runs up hill.
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Old Apr 28th 2017, 05:05 AM   #3
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Oh, of course!

power = ((0.5*0.015*3^2) + 0.015g*2) / 1.5 = 0.241W

Thanks ChipB
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