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Is it possible to have distance but apply no force?

  1. Dec 15, 2009 #1
    http://mail.google.com/mail/?ui=2&ik=73e979647b&view=att&th=125926df4ffe1738&attid=0.1&disp=inline&realattid=f_g25eq5it0&zw

    This is NOT homework.

    In the FBD above, there is no friction, the velocity is constant, and the distance travelled by the box is 10 m horizontally. Find the work exerted on the object horizontally.

    if f = 0, and a = 0 because of constant velocity,

    ΣFx = ma = Fapp (cos 40) - f
    200 kg (0) = Fapp (cos 40) -f
    0 = Fapp (cos 40) - f
    Fapp (cos 40) = f = 0

    thus,

    Fapp (cos 40) = 0

    does this mean: Work = Fapp (cos 40) (d)
    W = 0 (10 m)
    W = 0

    is this possible, to have no force but achieve distance?

    Hi, by the way, Im new here. :)
     
  2. jcsd
  3. Dec 15, 2009 #2

    Doc Al

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    Staff: Mentor

    I can't view your image (you'll have to post a link to an image hosting site or upload it as an attachment). But if something's moving with constant velocity, the net force on it is zero and thus the net work on it is zero.

    Can something move with no forces acting on it? Of course! Force is not required to maintain velocity, only to change it. See Newton's 1st law.
     
  4. Dec 15, 2009 #3
    oh. so does this mean there is no work applied at all? i find that peculiar.
     
  5. Dec 15, 2009 #4

    Doc Al

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    Staff: Mentor

    I can't see your FBD so I don't know what forces act. But certainly there's no net work done.
    Why is that?
     
  6. Dec 15, 2009 #5
  7. Dec 15, 2009 #6

    russ_watters

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    Staff: Mentor

    I see the diagram - yes, you've done the math correctly (after a quick look...). Yes, if you have constant speed motion that means there is no net force and therefore no net work done on the object.
     
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