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: Pulley problem involves Friction static and Kinetic problem

  1. Oct 3, 2009 #1
    1. The problem statement, all variables and given/known data

    M1 has a mass of 6.51 kg. It is on a horizontal surface, connected by a light string to a hook. Mass M2 can be increased smoothly by adding masses little at a time. The pulley has a negligible mass and no friction.

    When M2 is 3.12 kg it begins to accelerate downwards at a rate of 1.52 m/s2. Calculate mu static -mu kinetic for M1 on the surface.

    I was also given this hint, First calculate ms (from knowing the force it takes to begin moving) and then mk (from the given acceleration) and subtract

    2. Relevant equations

    F= Ma

    Fnety = T-Mg


    Fnetx= T-Fstatic

    Fs= Mus*Fn

    Fk= Muk* FN

    3. The attempt at a solution

    Fnety = T-Mg
    -4.74N= T-30.576N
    T= 25.83


    Fnetx= T-Fkinetic
    9.89N= 25.83-15.934
    Fk= Muk*Fn
    15.9348/63.798= 25.83

    Muk= .24976


    Fs= Mus* FN

    25.836= Mus * FN


    Mus-Muk= .155

    Attached Files:

  2. jcsd
  3. Oct 3, 2009 #2


    User Avatar
    Homework Helper

    There is something odd about this solution and I can't quite pin it down. I think you are supposed to write F = ma for each mass as your starting point. This would give you 2 equations:
    [1] T - u*m1*g = m1*a and [2] m2*g - T = m2*a
    where T is the tension in the string between the two masses.
    When a = 0, you get T = u*m1*g from [1] and when you put it into [2] you have m2*g = u*m1*g which gives u = m2/m1 = 0.479 for the static coefficient.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook