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# M2 - What does this mean... watch

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1. 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??
2. 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.
3. (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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