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

What should be the free body diagram?

  1. Oct 21, 2011 #1
    1. The problem statement, all variables and given/known data
    The Question gives some data, and a figure to find out the acceleration.
    In the arrangement shown (refer attachment) shown, M1=20kg, M2=30Kg, floor is smooth and friction between two blocks: μ(s) = 0.6, μ(k) = 0.4.
    F= 400N
    What are the forces acting on the two blocks?
    2. Relevant equations

    3. The attempt at a solution
    On M1, there is F acting towards right, and the friction towards the left.
    For M2, There is the friction acting towards right, and then the forces exerted by the pulleys.
    In what direction and magnitude do they act?

    Attached Files:

    • A.bmp
      File size:
      35.7 KB
  2. jcsd
  3. Oct 21, 2011 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    I'm assuming the pulleys are frictionless and have negligible mass.

    Then the tension in the rope in all locations is F .

    Forces exerted on the upper pulley: The rope exerts a force (equal to F) downward and a force, F to the left.

    Forces exerted on the lower pulley: What do you think?

    The pulleys may be considered as part of Block 1 .

  4. Oct 21, 2011 #3
    The force by the pulley on the lower block will be F towards the right, and F downwards.
    Meaning that in the direction parallel to the floor, only the reaction of the friction force between M1 and M2 will act on M2,to the right, right?
  5. Oct 22, 2011 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    So the net force that the rope exerts on block #2, via the pulleys, is zero.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook