# Homework Help: Conservation of energy

1. Mar 17, 2009

### Knfoster

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. Mar 17, 2009

### 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.)

3. Mar 17, 2009

### Knfoster

How do I go about finding the time? Is there a certain equation that I need?

4. Mar 17, 2009

### Knfoster

Do I use one of the four equations for motion?

5. Mar 18, 2009

### Staff: Mentor

What's the definition of power?

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