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Homework Help: Block on slop compressing spring.

  1. Oct 31, 2008 #1
    1. The problem statement, all variables and given/known data
    A spring can be compressed 2.0 cm by a force of 271 N. A block whose mass is 20.0 kg is released from rest at the top of a frictionless incline as shown, the angle of the incline being 30.0°. The block comes to rest momentarily after it has compressed the spring by 5.5 cm. How far has the block moved down the incline at this moment? What is the speed of the block just as it touches the spring?

    m = 20kg
    2. Relevant equations

    K = 1/2mv^2
    vf^2 = vi^2 -2a(xf-xi)

    3. The attempt at a solution

    How far has the block moved down the incline at this moment?
    First I found K to be 271N/2cm =13550 N/m, but I'm not sure if that matters for anything

    ax = mgcos([tex]\Theta[/tex] - mgsin[tex]\Theta[/tex])/m
    (20*9.81cos30 - 20*9.81*sin30)/20kg = 3.59 m/s^2

    I tried plugging this into vf^2 =vi^2 -2a(xf-xi) but then I realized that I don't have the initial velocity.

    I'm very confused, can someone please give me a tip or some advice on what to try. I would try to find the distance to just before the spring, but I don't even know what to do since the only thing i have is the acceleration.

    I would greatly appreciate some tips or advice for what I should try. Thanks
  2. jcsd
  3. Oct 31, 2008 #2
    Try using energy conservation. That's usually more straightforward than using forces.
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