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Homework Help: Need help on physics problem

  1. Nov 2, 2004 #1
    A car jack is used to lift a quarter of the weight of a 1200kg car 20 cm in 20s. Calculate the power of the car jack.

    I got this answer no problem:
    P = eg/t
    = mgh/t
    = (300kg)(9.8N/kg)(0.20m)/20.0s
    = 588J/20.0s
    = 29.4W

    I believe this is a follow up question and I can't seem to get it. I get an answer, but it's different fromt he back of the book so I guess this answer is wrong. Maybe you can help me on this question:

    A 250-W hydraulic car jack is used to do the same work on the same car as in the previous problem. How long will it take to lift the car this time?
  2. jcsd
  3. Nov 2, 2004 #2
    Since the work will be the same, then