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Box sliding down wall at constant speed

  1. Mar 2, 2015 #1
    1. The problem statement, all variables and given/known data
    The 2.0 kg wood box in the figure slides down a vertical wood wall while you push on it at a 45 ∘angle.
    https://session.masteringphysics.com/problemAsset/1070374/4/06.P51.jpg

    2. Relevant equations
    ΣFY = FPY - mg

    3. The attempt at a solution
    I know that since there is a constant velocity, the acceleration will be zero. I then have
    0 = FPsin45 - mg
    FPsin45 = mg
    FP = (mg)/sin45
    FP = ((2kg)*(9.8m/s2))/sin45
    FP = 27.719 N

    Which is wrong. Am I correct in assuming that the only forces in the Y direction (taking up as positive Y) are the y-component of the pushing force and gravity? What am I missing here?
     
  2. jcsd
  3. Mar 2, 2015 #2
    Your approach just misses the friction component which acts against the relative motion of box/wall (i.e. downwards).. Therefore the equation will be

    F(push)sin45 - mu*N - mg = 0 ; where mu is coefficient of friction and N= F(push) cos 45 ...
     
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