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Homework Help: Conservation of Energy

  1. Oct 12, 2016 #1
    1. The problem statement, all variables and given/known data
    A mass is suspended from a crane by a cable of length L. The crane and the mass is moving at constant speed V. The crane stops and the mass on the cable swings out.

    What is the angle that the mass swings?
    If the angle is 50 degrees and L=6m, what is the initial speed of the crane?

    2. Relevant equations

    3. The attempt at a solution
    For the first part where it asks for the angle, since no numbers are given I assume they're just asking for the equation. My attempt at this is using the equation PE=mgh where h=L(1-cosθ) so it'll be PE=mgL(1-cosθ). The second part for the initial speed can be solved by (PE + KE)initial =(PE+KE)final.
  2. jcsd
  3. Oct 12, 2016 #2


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    Science Advisor

    It's likely you're expected to express θ in terms of L and V (and g), m will cancel out. You'll use the same equation you will for the second part.

    Yes, just plug and chug.
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