# Homework Help: Work, Average Power, and Time?

1. Oct 8, 2009

### luvlybug1025

1. The problem statement, all variables and given/known data

Determine the time it takes to climb three flights of stairs (height = 9.7m). Compute the work done against gravity. Compute the average power expended in watts and in horsepower.

Person = 150lbs.

2. Relevant equations

h = 9.7m
4.45N/1lb
Avg Power = change in W/change in t
1hp = 746W
F=ma
W = F * d

3. The attempt at a solution

Ok...so, my 150lb=667.5N. That's my F now.
W = f * d = 667.5N * 9.7m = 6474.75J
Once I can find the time it took, then I can use that and the work to find the average power. I just can't figure out how to get time traveled from Work done. Am I on the right track?

2. Oct 8, 2009

### kuruman

You are on the right track. Since the time is not given, you have to come up with a reasonable estimate or climb three flights of stairs and time yourself.

3. Oct 8, 2009

### luvlybug1025

Wow, that makes sense. (I had to measure the stairs myself to.)
Thanks very much for replying so quickly!
I got 21.33s
Work = 5303.8J
Power = 248Watts = 0.332hp
That seems reasonable, right?

4. Oct 9, 2009

### kuruman

Pretty reasonable.

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