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

Moving blocks problem

  1. Oct 21, 2011 #1
    1. The problem statement, all variables and given/known data

    I'm stuck on this one,

    A 32.5-kg block (m1) is on a horizontal surface, connected to a 6.9-kg block (m2) by a massless string as shown in the Figure. The pulley is massless and frictionless. A force of 223.3 N acts on m1 at an angle of 30.1o. The coefficient of kinetic friction between m1 and the surface is 0.213. Determine the upward acceleration of m2.

    2. Relevant equations

    3. The attempt at a solution
    I determined the net force on m1 as follows

    F=223.3Cos(30.1)-(m1*g-223.3Sin(30.1))*.213 - m2*g.

    Then I determined the acceleration of m1 by dividing the net force by 32.5kg. I assumed that the acceleration of m1 and m2 should be the same so i got an answer of 2.51 m/s^2.

    The online homework says this is wrong, what am I missing?

  2. jcsd
  3. Oct 21, 2011 #2
  4. Oct 21, 2011 #3
    Here it is

    Attached Files:

  5. Oct 21, 2011 #4
    Why is the term m2*g in the above equation?
  6. Oct 21, 2011 #5
    The weight of m2 creates tension on the rope, which exerts a rightward force on m1, so don't you have to factor that into the net force on m1? m2*g is the weight of m2.
  7. Oct 21, 2011 #6
    The above is correct but the rest of the statement is not correct.

    You will see why it is not correct if you consider m2. Is not m2 accelerating upwards?
  8. Oct 22, 2011 #7
    Thanks! got it.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook