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M2 - What does this mean... watch

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    There is a question in an M2 paper (June 08) where a particle slides down a rough ramp. Part (a) for 5 marks is "Find the total energy lost in traveeling from A to B" What does this exactly mean? I thought it was the energy lost due to friction so ΔGPE - ΔKE. but this seems to be wrong as the answer, i think, is ΔGPE + ΔKE... But shurley this energy isn't 'lost' it is, well nothing really is it??
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    There are two types of energy the particle can have at the different positions. GPE, or KE. You need to work out the KE at A (if it is moving) and also the GPE energy it has ABOVE B. So take the height of B as GPE=0 and construct a triangle to work out the height of A above B. Then work out the GPE of the particle at A. Altogether, the total energy of the particle at A will be it's GPE and KE at that point. Then work out the energy at B, it's GPE will be 0 (if you set B as your arbitrary point) and work out it's KE. So the total 'loss' in energy of the particle is equal to the total energy at A - total energy at B. This basically boils down to being ΔGPE + ΔKE. Of course, overall, no energy is lost, the energy has gone into overcoming friction, usually dissipated as heat.
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    (Original post by Noble.)
    There are two types of energy the particle can have at the different positions. GPE, or KE. You need to work out the KE at A (if it is moving) and also the GPE energy it has ABOVE B. So take the height of B as GPE=0 and construct a triangle to work out the height of A above B. Then work out the GPE of the particle at A. Altogether, the total energy of the particle at A will be it's GPE and KE at that point. Then work out the energy at B, it's GPE will be 0 (if you set B as your arbitrary point) and work out it's KE. So the total 'loss' in energy of the particle is equal to the total energy at A - total energy at B. This basically boils down to being ΔGPE + ΔKE. Of course, overall, no energy is lost, the energy has gone into overcoming friction, usually dissipated as heat.
    ahh i see, thanks
 
 
 
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