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Force over a frictionless Surface

  1. Jan 27, 2012 #1
    Hey,

    A certain problem in my physics textbook states that a person pushes a crate over a frictionless surface with a constant force.

    If the crate accelerates, wouldn't the person eventually have to start running with it in order to keep applying force to it?
     
  2. jcsd
  3. Jan 27, 2012 #2

    PhanthomJay

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    Yes. But he wouldn't be able to, because he'd fall on the ice first.:wink: Perhaps he could push it with constant force from a chopper. Or just let go of the crate and let it move at some constant speed (neglecting resisting forces like air).
     
  4. Jan 27, 2012 #3
    Deleting a trivial response
     
    Last edited: Jan 27, 2012
  5. Jan 27, 2012 #4

    ZapperZ

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    Physics is difficult enough as it is without worrying about things that really do not matter in trying to understand and tackle this problem. I suggest you concentrate on what really matters.

    Zz.
     
  6. Jan 27, 2012 #5
    I like your query and will re-post my original response..... he could push with a long stick. I have tried to think of other ways and I am still thinking about it (have lots of time)
    To raise the level I would add that conservation of momentum could be used to analyse the resulting motion and I believe that the centre of mass of the system would remain fixed.
    However, I do not know what really matters in physics.
     
    Last edited: Jan 27, 2012
  7. Jan 27, 2012 #6

    AlephZero

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    @#2, #5: The OP's question doesn't say the person is also standing on the frictionless surface. Think about pushing a crate along a roller track, for example.

    Also, what ZZ said.
     
  8. Jan 27, 2012 #7
    If he is standing on the frictionless surface this becomes a very interesting physics problem !!!!!
     
  9. Jan 27, 2012 #8
    You could attach a string to the far end of the crate, pass it over a frictionless, massless pulley, pull the string back with an attached spring ensuring that the spring extension is constant.
    It is a common mistake to assume that you could attach a mass to the string and expect its weight to provide a constant force. Don't get caught by that nDever !!!!
     
  10. Jan 27, 2012 #9
    you could tilt the frictionless surface to 30 degrees then the object would experience a constant force of 0.5W (W = weight of crate) down the slope WITHOUT the person touching the crate.......ZZZZZZZ
     
    Last edited: Jan 27, 2012
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