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Work and Power problem

  1. Mar 3, 2016 #1
    1. The problem statement, all variables and given/known data

    A girl (starting from rest) is pushing a cart full of softballs at an angle of 30 degrees above the horizontal. She pushes with a force of 150N. She travels through the school store for 20 minutes and travels a total of 800meters.

    a). How much work (in joules) does she do?

    b). What is average power (in watts) over the entire time?

    2. Relevant equations
    W=Fdcos(theta), P=W/t, W=J/s

    3. The attempt at a solution
    For part a) I did W=Fdcos(theta) and got 103,923J and for part b) I'm not sure how to write the units because it is in minutes so I just converted 20 minutes to 1200 seconds and got 87 watts, I just don't think I did everything correct because of the large numbers and the units have confused me.
     
  2. jcsd
  3. Mar 3, 2016 #2

    andrewkirk

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    Your calculations look correct to me. The result of 87 watts is a reasonable power output for a schoolgirl working comfortably below maximum effort.
     
  4. Mar 3, 2016 #3
    Were all my units correct because the question asked for specifics and that is what confused me?
     
  5. Mar 3, 2016 #4

    andrewkirk

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    Yes the units are correct. The base SI units are metres, seconds and kilograms. A Joule is one Newton metre, a Newton is one ##kg\ ms^{-2}##, and Watt is one Joule per second. Calculations should be in SI units except where specified otherwise, and that's what you've done. Hence for instance your conversion of minutes to seconds was the correct thing to do.
     
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