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Homework Help: Conservation of Energy in different frame

  1. Nov 20, 2007 #1
    A train moves in a straight at a constant speed u. A boy on the train throw a ball of mass m straight ahead, along the motion of the train, with a speed v with respect to himdelf.
    a)What is the KE gain of the ball measured by the boy?
    b)What is the KE gain of the ball measured by a man standing by the railroad track?
    c)How much work is done by the boy throwing the ball?
    d)How much work is done by the train?

    a) 1/2 mv^2

    b) 1/2m(v+u)^2 - 1/2 mu^2 = 1/2mv^2 +muv

    c) measured by the boy: 1/2 mv^2 , measured by the man: 1/2 mv^2

    d) measured by the boy: 0 , measured by the man: muv

    My fd suggest that there is no workdone by the boy measured by the man, all work is done by the train.

    Is there anything wrong in part c and d?
    Plz tell me why if I am wrong
  2. jcsd
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