1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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.

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

Have something to add?
Draft saved Draft deleted