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Homework Help: Newton's law application

  1. Mar 23, 2004 #1
    hey guys! i need some help, a big help. this is urgent... can somebodyhelp me solve this problem:

    what force, applied parallel to the plane, is necessary to move a 16 kg object up africtionless palne with a uniform acceleration of 2.0 m/s2 if the plane makes an angle of 60 degrees with the horizontal?

    pls somebody help me. i really need it badly. hope somebody would reply today. thanks...
  2. jcsd
  3. Mar 23, 2004 #2
    Is the plane on the surface of earth, so that the body is subject to a gravitational force of (16 kg)*(9.8 m/s^2)?

    Is the acceleration wrt the plane or the ground? Makes a big difference.

    I assume the answers are yes and wrt the plane.

    The NET force necessary to move the body 2 m/s^2 is simply mass * acceleration = (16 kg)*(2 m/s^2).

    However, you need more than that to overcome the gravitational force. The body is kept from moving straight down by the plane, so it would only go down the plane with a force of (16 kg)*(9.8 m/s^2)cos 30 degrees. Reverse that force and add to the above ("NET").

    Now, I may have made a mistake somewhere, so go over that solution carefully. Don't blame me, it was a rush job, right, boss? :smile:
  4. Mar 26, 2004 #3

    Doc Al

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    Staff: Mentor

    The component of the object's weight parallel to the plane is [itex]mg\sin\theta[/itex] acting down the plane. The applied force F (acting up the plane) must be enough to overcome that and produce the needed acceleration:
    [tex]F = mg\sin\theta + ma[/tex]
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