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Work and force problem (piano moving on an incline)

  1. Dec 1, 2009 #1
    1. The problem statement, all variables and given/known data

    A 280-kg piano slides 4.3 m down a 30 degree incline and is kept from accelerating by a man who is pushing back on it parallel to the incline. The effective coefficient of kinetic friction is .400. Calculate:

    (a) the force exerted by the man,
    (b) the work done by the man on the piano,
    (c) the work done by the friction force,
    (d) the work done by the force of gravity, and
    (e) the net work done on the piano.


    2. Relevant equations

    W=Fd.... ?

    3. The attempt at a solution

    I know it's a long problem... I don't know how to find the work done by each force.
     
  2. jcsd
  3. Dec 1, 2009 #2

    Delphi51

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    Homework Helper

    You will need to find the components of the gravitational force that are along the ramp and normal to the ramp. Then you can find the force of friction.
    The work done by any force is W = F*d.
     
  4. Dec 1, 2009 #3
    a) Do I use mu*mg*cos(angle) - mg*sin(angle) ...?

    If so, I did .40(280)(9.8)cos(30) - 280(9.8)sin(30) = -421.5 N
    (Isn't it negative because it's going down?)


    b) For this answer I did -421.5*4.3 and got -1812.45 J

    I'm still trying to figure out the rest...
     
  5. Dec 2, 2009 #4

    Delphi51

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    Looks okay, though I would have reversed the signs for the (a) calculation - the friction term reduces the force. But I agree with the minus sign in (b) since the piano is pushing on the man.
     
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