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Homework Help: Am I doing this problem correctly?

  1. Apr 8, 2008 #1
    1. The problem statement, all variables and given/known data

    a) A 50 g ice cube can slide without friction up and down a 30 degree slope. The ice cube is pressed against a spring at the bottom of the slope, compressing the spring 10 cm. The spring constant is 25 N/m. When the ice cube is released, what total distance will it travel up the slope before reversing direction?

    b) The ice cube is replaced by a 50 g plastic cube whose coefficient of kinetic friction is 0.20. How far will the plastic cube travel up the slope?

    2. Relevant equations
    change in thermal energy= (force of kinetic friction)*(displacement)

    3. The attempt at a solution
    I got part a, and I want to make sure I am doing part b correctly.

    Here's what I did.

    Fk= mgcostheta * coefficient of friction
    Fk= (.05kg)(9.80)(cos30)(.20)=.085 N

    change in thermal energy= Fk* distance covered up slope (d)
    change in thermal energy = .085 * d

    I called y the final height so y=dsin30

    Kf + Uf + change in thermal energy = Ki + Ui

    (.05kg)(9.80)(dsin30) + (.085d) = (.5)(25 N/m)(.1m)^2
    d= .379 m = 37.9 cm
  2. jcsd
  3. Apr 8, 2008 #2


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    Science Advisor
    Gold Member

    Looks good.
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