Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook