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Homework Help: Find the force on an object on an inclined plane

  1. Aug 19, 2008 #1
    1. The problem statement, all variables and given/known data

    A body is projected up an inclined plane with a speed Vo. The inclination of the incline is [tex]\theta[/tex]. The surface of th incline is a tangent to a circle of radius R. Find the force acting on th object when it is at the top of the sphere provied that Vo= 2*the minimum velocity need to reach the top of the sphere.
    The length of incline = L
    Assume that the block does not lose contact with the track.
    3. The attempt at a solution
    The minimum velocity required, as I calculated was:
    [tex]\sqrt{2g[R(1-cos \theta)+ L sin \theta}[/tex] which was correct.
    But the Force I calculated was diffrent.

    At the top of the phere, the velocity will become Vo/2. Why oesnt (mV^2)/R give me the correct answer? as the body perform circular motion. Help me please.
  2. jcsd
  3. Aug 20, 2008 #2
    Last edited by a moderator: May 3, 2017
  4. Aug 20, 2008 #3


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    Homework Helper

    Re: Force

    The minimum velocity required to reach the top satisfies (1/2)mv0^2=mgh (where h is the total height of the top of the sphere) - use conservation of energy. If you leave with twice that velocity your energy at the top is (1/2)m(2*v0)^2-mgh. Equate that to kinetic energy at the top and solve for velocity. You DON'T arrive with half the initial velocity.
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