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Conservation of engery and work 2.

  1. Apr 11, 2012 #1
    ben carries a 200N suitcase up three flights of stairs total vertical distance of 10.0m and then pushes the suitcase with a horizontal force of 50.0 N at a constant speed of 50 m s for a horizontal of 35.0 m across the 3rd floor how much work does Ben do on the suitcase during this entire motion

    Total work done by Ben = mgh + F*s = 200 * 10 + 50 *35 = 2000 + 1750 = 3750 Joules.

    i have a feeling this is wrong i really need help!!
     
  2. jcsd
  3. Apr 11, 2012 #2

    berkeman

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    Staff: Mentor

    That's close. You left out the acceleration of gravity when you plugged in the numbers.

    It helps to carry units along in your equations -- if you had, you would have noticed that the units were not Joules when you calculated just mh instead of mgh.

    Try again (with units this time)?
     
  4. Apr 11, 2012 #3
    yeah well 200 n includes the 9.81 so i dont need to include it again right?
     
  5. Apr 11, 2012 #4

    berkeman

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    Whoops! You are right!
     
  6. Apr 11, 2012 #5
    okay so heres what i did

    200N x 10m + 50 N x .5om/s = 2025
     
    Last edited by a moderator: Apr 11, 2012
  7. Apr 11, 2012 #6
    and i think i typed the velocity wrong in the question is should be .50 m/s
     
  8. Apr 11, 2012 #7

    berkeman

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    No, you had it right the first time. When pushing the object, the work is force X distance. The units of work are Newtons * meters, not Nm/s.
     
  9. Apr 11, 2012 #8
    ohh kk .. why did they give me the velocity then.. doesnt that mean i have to use it?
     
  10. Apr 11, 2012 #9

    berkeman

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    Nope. Not to answer the question they gave you.
     
  11. Apr 11, 2012 #10
    Last edited by a moderator: Apr 11, 2012
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