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Homework Help: Calculating Velocity Using Power

  1. Jul 18, 2013 #1
    1. The problem statement, all variables and given/known data
    The problem I'm working on gives the total power (100 W) that will be exerted by a man (80 kg) climbing a set of stairs(r = 8mi + 4mj). It would like to know at what constant velocity he would have to move to achieve the given power.

    2. Relevant equations

    3. The attempt at a solution

    The difficulty I'm having is if he is moving with constant velocity there would be no acceleration and thus no force. So how could there be any power generated? I attempted to find the force the man would have to exert to overcome the force of gravity, which I found to be equivalent to the force of gravity (since they would have to sum to zero). But, when I use this I get a velocity that doesnt make sense (.2849 m/s). Have I got the wrong concept?
  2. jcsd
  3. Jul 18, 2013 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    But there is a force. It's called gravity.

    Compute the rate at which he gains potential energy as he climbs the stairs at a rate of 100W. This will equal mg dh/dt.
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