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Help with Kinetic Energy concept of two masses that move the same distance

  1. Dec 11, 2012 #1
    Help with Kinetic Energy concept of two masses that move the same distance!!

    ScreenShot2012-12-11at51940PM.png

    I don't understand why the answer to this is B :(

    Because KE = (1/2)mv2, if they move the same distance and have DIFFERENT masses, the kinetic energies would be different no?
     
  2. jcsd
  3. Dec 11, 2012 #2
    Re: Help with Kinetic Energy concept of two masses that move the same distance!!

    Don't forget that the KE depends on the speed of the blocks, not just the masses and certainly not (at least not explicitly) the distance they move.
    Hint: consider instead the amount of work done by the force on the masses.
     
  4. Dec 11, 2012 #3
    Re: Help with Kinetic Energy concept of two masses that move the same distance!!

    Oh ok I think I understand...
     
  5. Dec 11, 2012 #4

    haruspex

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    Re: Help with Kinetic Energy concept of two masses that move the same distance!!

    It's natural to assume that the force is applied for the same duration to each, but you are not told that. In fact, it cannot be so. Hence, the speeds can be different although the distances are the same.
     
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