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Homework Help: What is the speed of the crate when it reaches the bottom?

  1. Feb 12, 2010 #1
    1. The problem statement, all variables and given/known data
    A 20.0-kg crate slides down an inclined plane that is 3.00-m high and 20.0-m long. If friction is negligible, what is the speed of the crate when it reaches the bottom of the plane?

    2. Relevant equations
    W= F*D
    K= 1/2 m*(v^2)

    3. The attempt at a solution
    They don't give me an angle so I'm not sure how I'm supposed to go about solving for the force parallel to the inclined plane. Once I have that I'll be able to finish out the problem. Help please!
    (The answer turns out to be 7.67 m/s; I just need to know how to get there)
  2. jcsd
  3. Feb 12, 2010 #2
    Just use conservation of energy. You have gravitational potential energy in the beginning. Don't bother with the work [tex]W=FD[/tex].
  4. Feb 12, 2010 #3
    Ahhh, ok I see. Thanks alot N-gin!
  5. Oct 18, 2010 #4
    The 20 M long is not needed for this problem because the friction is assumed to be zero. No energy is lost in friction and so M*g*H = (1/2)*M*V^2

    So V = sqrt(2*g*H)

    So the velocity is independent of the Mass!!!

    If you had friction, then still mass is irrelevant.
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