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Homework Help: Which has greater momentum?

  1. Nov 18, 2006 #1
    Please check over my work

    Two bodies of unequal mass, placed at rest on a frictionless surface, are acted on by an equal horizontal forces for equal times. Just after the forces are removed, the body of greater mass will have:
    The body of greater mass will have the the greater speed, the greater acceleration, the smaller momentum, the greater momentum, or the same amount as the other body.

    Would the answer be the larger body would have the same amount amount of momentum as the other body because P(before)=P(after). The momentum would have to come out the same in order for that to be right.

    second question:

    A 0.2kg rubber ball is dropped from the window of a building. It strikes the sidewalk below at 30m/s and rebounds up at 20m/s. The impulse during the collision would be:

    my work:
    0.2 (-30m/s) - 0.2 (20m/s) = 10 upward

    Please let me know if I am on the right track and let me know where I might have gone wrong:redface:
  2. jcsd
  3. Nov 18, 2006 #2


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    Homework Helper

    Yes, but you should use the fact that the impulse of the force equals the change of momentum, and since the impulse is equal for both bodies, you have F*t = m1v1 = m2v2.

    Looks good.

    Edit: the change in momentum (i.e. the impulse) should actually be: [tex]0.2\cdot 20\vec{j}-0.2\cdot(-30)\vec{j}=10\vec{j}[/tex], which means 10 upwards.
    Last edited: Nov 18, 2006
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