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 Wm g v t e == = power time force exerted speed time bg a f a f a f where t h vn h s = + as above. Thus, W mgvh h 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: WW W mgnhh h mgvh h mgh nh v h mgh e s ss s s =+ = + + + = + + = person P7.53 (a) Km v W =− = 1 2 0 2 , so v W m 2 2 = and v W m = 2 (b) WF d F W d xx =⋅= ⇒ = Fd *P7.54 During its whole motion from y = 10 0 . m to y 320 . m m , 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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