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Homework Help: How much work was done aginst friction?

  1. Mar 26, 2006 #1
    Hello I am having toruble solving this problem. I would appreciate any help.

    A 75 N block is pushed at 5.0 m/s up a ramp 6.0 m long to a platform 2.0 m high. If the coefficient of friction is 0.300
    a) how much work was done?
    b) how much work was done aginst friction?
    c) how much work was done against gravity?
    d) how much power was developed?

    I solved for theta using trig and got 19 degrees.
    Then I solved for work with the equation [Fw(sintheta+ucostheta)]h and got 91J.
    I am confused on how to solve for the work against friction and the work aginst gravity though.
    Thanks for any help
    Last edited: Mar 26, 2006
  2. jcsd
  3. Mar 27, 2006 #2
    ok here is the way to proceed

    first draw the free body diagram for it

    you will get the following things from it
    1) weight mg(75 N) acting downwards
    2) then normal reaction mgcos(teta)
    3) the force 0.3*R(normal reaction)

    now solve for it using
    where f is the force required to move up
    where s is the distance moved , use trignometry and u will get it
    the work according to me is 135J

    c)then for the work done against gravity,to reach the topest point u will need mgh J where h is 2 m in ur case

    b)from the total work done subtract this and u will get the work done against friction

    d) use P=FV
    where F is the force to move up and v is velocity given(5 m/s)

    hope this helped u. please tell me If i am wrong.
  4. Mar 27, 2006 #3
    note keep the trigrometic values in fraction itself dont find the angle
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