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Homework Help: Physics 101 Questions

  1. Oct 25, 2007 #1
    1. The problem statement, all variables and given/known data
    For each of the following statements determine whether it is correct or incorrect.

    A.The work done to raise a box onto a platform depends on how fast it is raised.

    B.The kinetic energy is independent of the reference frame of the observer.

    C.The kinetic energy of an object depends on the direction of the motion involved.

    D.The kinetic energy can never be negative.

    E.Spring A and B are identical except that A is stiffer than B; that is kA > kB. More work must be expended on spring A if both springs are stretched by the same amount.

    F.If the Earth revolves around the sun in a perfectly circular orbit, then the sun does work on the Earth.

    2. Relevant equations

    3. The attempt at a solution

    Which one(s) are wrong?? I thought I had them right but I don't.
  2. jcsd
  3. Oct 25, 2007 #2


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    C is wrong.
  4. Oct 25, 2007 #3
    Kinetic Energy can never be negative, so does it matter in which direction the object is moving?
  5. Oct 25, 2007 #4
    oooo duh lol.
  6. Oct 25, 2007 #5
    If kinetic energy depended on direction, then if it went in the opposite direction of the 'positive vector', it would be negative which is not possible.

    There is no definite positive vector. Kinetic energy is energy. If energy was lost by dropping an object from a hight because the positive direction for kinetic energy was diagonal to the ground, then it would generally mean that by changing the direction, you are somehow creating heat.

    Anyway, in real life, how would one specify in what direction the kinetic energy SHOULD be going?

    No, it does not matter which direction the object is moving.
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