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Homework Help: AP Physics Problem

  1. Nov 2, 2008 #1
    1. The problem statement, all variables and given/known data

    A 20 kg mass released from rest slides down a frictionless plane inclined at an angle of 30 deg with the horizontal and strikes a spring of spring constant K=200 newtons/meter. Assume that the spring is ideal, that the mass of the spring is negligible, and that mechanical energy is conserved. Use g = 10 m/s^2.

    a. Determine the speed of the block just before it hits the spring.
    b. Determine the distance the spring has been compressed when the block comes to rest.
    c. Determine the distance the spring is compressed when the block reaches maximum speed.

    2. Relevant equations

    a. V^2=Vo^2 +2ad
    b. PE spring = 1/2kx^2
    PE = mgh
    KE = 1/2mv^2
    PE +KE = PE spring
    c. Totally clueless

    3. The attempt at a solution
    For part a, I found what the force of gravity was in the x direction, divided by the mass, and then found the acceleration. Then I plugged that and the given variables into the kinematic equation

    V^2=Vo^2 +2ad

    And the answer I got was 7.75 m/s

    For part b, I tried Ug+K=Us, but I cannot determine the height so I do not know how to do this.

    Thanks for the help!
  2. jcsd
  3. Nov 2, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The amount of spring compression and the change in height are related by a little trig.
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