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Homework Help: Work and Energy of a mass

  1. Nov 2, 2008 #1
    1. The problem statement, all variables and given/known data

    Problem: Two objects of different mass start from rest, are pulled by the same magnitude net force, and are moved through the same distance. The work done on object A is 500 J. After the force has pulled each object, object A moves twice as fast as object B. (a) How much work is done on object B? (b) What is the kinetic energy of object A after being pulled? (c) What is the kinetic energy of object B after being pulled?

    2. Relevant equations

    [itex]W_n_e_t = \frac{1}{2}mv_2^2 - \frac{1}{2}mv_1^2[/itex]

    3. The attempt at a solution

    I believe that the answer to part (a) is 500 J also, since both objects are pulled through the same distance by the same force. I attempted to solve part (b) by using the above equation, but since I don't know the mass or the velocity, it didn't work out.

    If someone could help me, I would greatly appreciate it.
  2. jcsd
  3. Nov 2, 2008 #2


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    Science Advisor
    Homework Helper

    Hi Eternal Sky! :smile:

    ah … the whole point of the work-energy theorem … ∆W = ∆KE … is that you don't need to know how to calculate KE …

    (so you don't even need the whole of that equation of yours :wink:)

    you just calculate ∆W, and ∆KE is automatically the same!! :biggrin:
  4. Nov 2, 2008 #3
    Ah, I see. Thanks a lot for your help!
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