Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Friction problem Does this make sense?

  1. Aug 7, 2011 #1
    1. The problem statement, all variables and given/known data

    There are two masses stacked on top of each other. The bottom one, M, is attached to a spring with force constant k. The coefficient of static friction between the M and the top mass, m, is w. What is the maximum amplitude of oscillation such that the top box will not slip on the bottom.

    3. The attempt at a solution

    Initially my reasoning was that the force of friction, wn, where n is the normal force acting on the top box equal to mg, must equal the pulling force, f=kx

    wmg=kx then x=(wmg)/k. The answer in my book gives x= (w(m+M)g)/k

    I'm not sure if the way I arrived at that answer is correct:

    F=kx=(m+M)a ==> a1=kx/(m+M)

    wmg=kx ==>wg=kx/m=a2

    But a2 is really equal to a1 since that's the box that's what's being accelerated.

    wg=kx/(m+M) ==>w(m+M)g/k = x

    I just want to be sure that makes sense. Thanks for the help
  2. jcsd
  3. Aug 7, 2011 #2


    User Avatar
    Science Advisor
    Homework Helper

    Looks ok to me. You need the mass on the top not to slip at the point of maximum acceleration, which is when x is at its maximum value of oscillation.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook