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Homework Help: Three part weightlifter question

  1. Nov 13, 2011 #1
    1. The problem statement, all variables and given/known data

    A weightlifter works out at the gym each day. Part of her routine is to lie on her back and lift a 40kg barbell straight up at a distance of .50m.
    a. how much work does the weightlifter do to lift the barbell one time?
    b. if the weightlifter does 20 reps a day what total energy does she expend on lifting? assume 25% efficency.
    c. How many 400 calorie donuts can she eat a day to supply that energy.

    2. Relevant equations

    w=fd f=ma

    3. The attempt at a solution
    w=fd w=f*.50m
    f=40kg*a ???/
  2. jcsd
  3. Nov 14, 2011 #2
    Use the work energy theorem, the barbell has zero velocity at both the top and bottom of the rep.
  4. Nov 14, 2011 #3

    I like Serena

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    Homework Helper

    Your acceleration "a" is the acceleration of gravity: g=9.8 m/s2.
    With what you already have you should be able to find the work w...
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