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205_Physics ProblemsTechnical Physics

# 205_Physics ProblemsTechnical Physics - Chapter 7(b 207 The...

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Chapter 7 207 (b) The work done by the escalator is W mgvt e = = = power time force exerted speed time b ga f a fb ga f where t h v nh s = + as above. Thus, W mgvh v nh e s = + . As a check, the total work done on the person’s body must add up to mgh , the work an elevator would do in lifting him. It does add up as follows: W W W mgnhh v nh mgvh v nh mgh nh v v nh mgh e s s s s s = + = + + + = + + = person b g P7.53 (a) K mv W = = 1 2 0 2 , so v W m 2 2 = and v W m = 2 (b) W F d F W d x x = = = F d *P7.54 During its whole motion from y = 10 0 . m to y = − 3 20 . mm, the force of gravity and the force of the plate do work on the ball. It starts and ends at rest
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