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: Kinetic friction

  1. Oct 9, 2006 #1
    To move a large crate across a rough floor, you push down on it at an angle of 21°. Find the force necessary to start the crate moving, given that the mass of the crate is m = 32 kg and the coefficient of static friction between the crate and the floor is 0.57.

    N=mg=(32)(9.81)= 313.92 * coefficaint of mew sub s=.57=178.9
    Ok, I think I did that right....only I'm not sure what to do with the 21° angle. I did 178.9cos(21)=167.0 but that's not right.
     
  2. jcsd
  3. Oct 9, 2006 #2
    Did you draw a diagram with the applied force resolved into x and y components? (BTW, that's where the angle comes in)
    Because in this case, N does not equal mg.
     
  4. Oct 9, 2006 #3
    Like this?
    Ny=N
    Fky=0
    Wy=-mgsin(21
    Nx=0
    Fkx=-mewk
    Wx=0
    I did Fk=mewkN=.57*(mgsin(21)=.57*112.5=64.12 I did somthing wrong...again...but I don't know what...
     
  5. Oct 9, 2006 #4
    where's the force of the push? It has both an x and a y component.
    But yeah, that's the sort of chart I had in mind. :grin:
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook