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Homework Help: How much power must you exert

  1. Apr 11, 2010 #1
    How much power must you exert to horizontally drag a 20.0 kg table 14.0 m across a brick floor in 40.0 s at constant velocity, assuming the coefficient of kinetic friction between the table and floor is 0.600?

    2. Relevant equations

    P=F(d/t), fk=mukN

    3. The attempt at a solution

    P=(20.0*9.8)(14.0/40.0) fk=(0.600*20.0*9.8)
    =68.6W =117.6

    117.6-68.6=49W



    I really do not know how to do this problem, I just tried it in a way that made some sense to me, but it's obviously wrong. PLEASE HELP!!!
     
  2. jcsd
  3. Apr 11, 2010 #2
    When you drag something horizontally, you must do work to overcome the force of friction, not gravity.

    your first equation P = F (d/t) tells you the power needed to push something with a force F, that's moving in the direction of that force with a constant speed v = d/t

    The second equation [itex] F_k = \mu_k N [/itex] tells you how big the friction is if you know the normal force N
     
  4. Apr 11, 2010 #3
    So then do i need to find the work first and then whatever value I get from that use it to find the Power by using P=W/t?
     
  5. Apr 11, 2010 #4
    You can do that, or calculate the speed first and then Power = force * speed.

    The equation you gave P = F (d/t) does this all at once.

    The important thing is to calculate the force you must exert first.
     
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