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Momentum Concepts

  1. Feb 26, 2006 #1
    Can anyone help to clear these up for me ?

    If you have a wedge on a horizontal frictionless surface, a block starts from rest and slides down the inclined surface of the wedge, is rough. During the motion of the block the center mass of the block and wedge ---
    - would it be moving horizontally with increasing speed ?

    and...

    Two bodies of unequal mass are at rest on a frictionless surface, and are acted on by equal forces for equal times. Just after these forces are removed, the body with greater mass will...
    - greater acceleration or speed, or smaller momentum?
    For this one i want to say greater acceleration but can anyone explain if this is right ?
     
  2. jcsd
  3. Feb 26, 2006 #2

    Hootenanny

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    For your first question, yes, the centre of mass of the body would be accelerating horizontally in the opposite direction to the motion of the block.

    (2) For this question, think about the relationship [itex] F = ma [/itex].
     
  4. Feb 26, 2006 #3
    With all due respect I believe your answer for the first question is incorrect. There are no net external forces (in the horizontal direction) acting on the block-wedge system. Thus the momentum of the overall system will be conserved, and the CM will stay where it is.

    -Dan
     
  5. Feb 26, 2006 #4

    Hootenanny

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    Yes, my apologies, I've misunderstood. Just for my piece of mind, what would happen when the block left the wedge?
     
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