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Homework Help: Force on 2 Masses

  1. Apr 26, 2009 #1
    1. The problem statement, all variables and given/known data

    Two blocks, of mass M and m, are in contact on a horizontal, frictionless table (w/ the block of mass M on the left and block of mass m on the right). A force F1, is applied to the block of mass M and the two blocks move together to the right.

    a. Draw a FBD

    b. Suppose the larger block M exerts a force F2 on the smaller mass m. By N3, the smaller block m exerts a force F2 on the larger block M. Argue whether F1 = F2 or not.

    c. Derive an expression for the acceleration of the system.

    d. Derive an expression for the magnitude of the force F2 that the larger block exerts on the smaller block.

    e. Choose different values of M and m and compare the magnitudes of F1 and F2

    2. Relevant equations

    3. The attempt at a solution

    a. see attachment

    b. acc. to N3, "for every action, there's an equal and opposite reaction force" so F1 = F2 >> the thing is what if M is accelerating?

    c. a = Fnet/m

    d. F2 = ma

    ....is what i'm doing here...right?
    Last edited: May 28, 2009
  2. jcsd
  3. Apr 26, 2009 #2
    First off, if my hand was the force, the reactionary force is the force the block applies on my hand.

    Force depends on mass and acceleration. Aren't the blocks accelerating equally? And if they are of different masses how can the force on block 2 be the same as the one on block 1?

    First,expand Fnet and also the total mass is not m since there are two blocks of mass M and of mass m.
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