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Work Done on a Block on an Inclined Plane

  1. Mar 12, 2014 #1
    1. The problem statement, all variables and given/known data
    A block of mass m=18kg is pushed horizontally with a force of Fp=150N up an inclined plane of angle θ=32° and coefficient of friction of μ=0.10, a distance of x=5m. a) What is the work done by Fp. b) Work done by the gravitational force. c) Work done by the normal force.

    2. Relevant equations
    W = ∫Fdl
    Force in the same direction as displacement.
    or W = F*x

    3. The attempt at a solution
    My main question is how is work affected by friction?
    This question is like a part 2 where the first one had no friction and this one does but i don't see how friction gets involved at all.

    a) The Fp has 2 components, one that moves parallel to the inclined plane and the other perpendicular to the plane. so Fpx=Fpcosθ. So including friction do i do W = (Fpx-Ff)*x or just W=Fpx*x or ?

    b) Wg=∫Fgdx = mgsinθ*x

    c) WN=∫FNdx = 0 = there is no displacement in the direction of the normal force.
  2. jcsd
  3. Mar 12, 2014 #2
    a) You got it with your second equation there. It's irrelevant whether you are fighting against gravity, friction, or little green men pushing back in the opposite direction. Work is work.

    b) and c) You got it. Friction only causes the block to accelerate slower.
  4. Mar 12, 2014 #3
    I believe i found the answer.
    There was a part d that i thought didn't apply but it did. d) asks for the velocity of the block after it moves those 5m. Using KE= net W i was able to find an answer using friction that also seems plausible.
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