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Homework Help: Conservation of energy of a trolley

  1. May 19, 2008 #1
    1. The problem statement, all variables and given/known data
    hello, I'm revising for my mechanics exam on thursday. I understand everything except this:
    This is a question on a pastpaper:
    The trolley and mass are joined by an inextensible string. In an experiment to investigate energy changes, the trolley is initially held at rest, and is then released so that the mass falls vertically to the ground.

    State what measurements would need to be made to investigate the conservation of energy
    -masses of trolley and falling mass
    -distance mass falls/trolley moves and time taken to fall

    Describe how the measurements would be used to investigate the conservation of energy:
    Answer(on markscheme):
    -calculate loss of gravit. pot. energy of falling mass (mgh)
    -calculate speed of trolley (distance/time)
    -calculate kinetic energy of trolley and mass
    Compare loss of potential energy and gain of KE

    2. Relevant equations
    everything is clear to me, except this part in red. Why do I have to calculate KE of trolley and mass?
    And how can I investigate the conservation of energy by comparing loss of PE and gain of KE?

    3. The attempt at a solution

    Is it probably like this:
    I calculate the loss of GPE of falling mass.
    than I calculate KE of mass
    and just compare both.

    What schould I get as a result?
    loss of GPE = gain of KE?

    hope someon ecan help me

  2. jcsd
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