# Power stairs problem

1. Nov 10, 2008

### sweedeljoseph

1. The problem statement, all variables and given/known data
How much power is needed for a 44 kg person to climb 12 flights of stairs that each have a height of 2 meters, in a time of 15 seconds?

2. Relevant equations
P=W/T

3. The attempt at a solution
answer from the teacher is 690 W. i remember doing the something like this in class but i dont remember exactly what all to do. wouldnt you multiply 12 by 2 so its total distance then multiply it by the 15 for the total time? or is that just time in general, the total? then put it into the power equation? i know youre supposed to convert the mass into N but thats it. im so lost please help me.

thank you!
sweedeljoseph

2. Nov 10, 2008

### asleight

$$U_0+W=U_f\rightarrow W=\Delta U$$. Then, use your relevant equation to solve.

3. Nov 10, 2008

### sweedeljoseph

whats U initial? or U final?

4. Nov 10, 2008

sweedeljoseph, there is probably more than one way to solve this. You have the key equation P=W/t

Yes, t is the TOTAL time

Now you just need to find the Work. Work is defined as Force*displacement

You found the displacement to be 24 meters.

What is the force in this case?

Casey

5. Nov 10, 2008

### sweedeljoseph

well force is in N and you can make the mass into newtons. mass is 44 kg so times 9.8 its 431.2 N. so im guessing thats the force?

i just put it in the calculator. it works! thank you. for some reason i kept thinking W was weight instead of work. i feel stupid haha.

thank you!
sweedeljoseph