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Conservation of energy

  1. Mar 17, 2009 #1
    1. The problem statement, all variables and given/known data
    A 54.2 kg student climbs a 6.95 m rope and stops at the top. What must her average speede in order to match the power output of a 110 W lightbulb?

    2. Relevant equations
    PE=mgh
    KE=1/2mv^2
    W=(Xf-Xi)(cos theta)(F)
    W= delta KE
    PE+KE = PE+KE (before and after)

    3. The attempt at a solution
    I know that the PE for the student is 3691.6 J at the top of the rope. And KE is zero at the top of the rope, so PE at the bottom of the rope would be 0, and KE would be 3691.6.

    I don't know what to do next and I don't know how to use the 110 W light bulb.

    Please help. Thank you.
     
  2. jcsd
  3. Mar 17, 2009 #2

    Doc Al

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    Staff: Mentor

    Good. This represents the work she must do to raise herself up the rope. Hint: How quickly must she climb the rope so that her power equals 110 W? (Find the time, then figure out her speed.)
     
  4. Mar 17, 2009 #3
    How do I go about finding the time? Is there a certain equation that I need?
     
  5. Mar 17, 2009 #4
    Do I use one of the four equations for motion?
     
  6. Mar 18, 2009 #5

    Doc Al

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    Staff: Mentor

    What's the definition of power?
     
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