Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Power stairs problem

  1. Nov 10, 2008 #1
    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. jcsd
  3. Nov 10, 2008 #2
    [tex]U_0+W=U_f\rightarrow W=\Delta U[/tex]. Then, use your relevant equation to solve.
     
  4. Nov 10, 2008 #3
    whats U initial? or U final?
     
  5. Nov 10, 2008 #4
    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
     
  6. Nov 10, 2008 #5
    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
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook