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Homework Help: Easy Energy Conservation. Spring, Incline/Ramp, Friction.

  1. Feb 26, 2010 #1
    1. The problem statement, all variables and given/known data

    Question for search purposes:

    A crate is placed against a compressed spring on an incline. When the spring is released, the crate moves up the ramp and comes to a stop.

    How far was the spring compressed?

    Hint: The mass and the spring may not be in contact at the end.

    13-2-q.png
    13-2-1.png
     
  2. jcsd
  3. Feb 26, 2010 #2

    cepheid

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    Your equation for energy conservation looks okay. I would have formulated it as:

    spring elastic potential energy lost = grav. potential energy gained + work done by friction

    which is a slightly more intuitive ordering to me.

    It looks like you forgot a factor of g in your expression for the normal force, which should of course end up having units of force, not mass.
     
  4. Feb 26, 2010 #3
    Thanks for your help. I agree that they were ordered funny -- but by the time I realized that, I was feeling too lazy to redo my diagram!

    Anyway, I tweaked some things, and now my answer is even further off! I am being tested on this Monday, so I appreciate the help...got to figure these concepts out!

    I just double and triple checked this for accuracy....I am getting exactly what my math is telling me I should get, so I must have set something up wrong or something.

    13-2-2.png

    Hold it -- duh. Hold it. Got my spring equation off a little.
     
  5. Feb 26, 2010 #4
    Solution

    13-2-3.png
     
  6. Feb 26, 2010 #5

    cepheid

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    Glad to see you sorted it out.
     
  7. Feb 26, 2010 #6
    Yeah, thanks for the help. It's hard to wander through the algebra forest looking for mistakes when you're not even sure your Physics is right ;)
     
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