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Homework Help: What acceleration of blocks in given condition.

  1. Jun 27, 2011 #1
    see this image

    something about question:=> a block M1 placed over M2 Nd M2 placed on the earth.A constant force F is applied in upward direction. You have to tell about the motion of M1 and M2 in condition as given below pulleys are frictionless and only friction is in between M1 and M2.

    first case In first case friction is zero between both blocks so will block M1 and M2 is zero.
    second case friction between M1 and M2 is very large.

    tell me about acceleration about the bodies in both cases if you think more variable required to answer then introduce them.
    My mind says that there will acceleration in Block M2 will something in second case but sometimes i think that acceleration of M2 will zero in both cases. I say there will acceleration in block M2 zero because force is in upward direction(this logic seeming wrong) but i think there will acceleration in block M2 because a force will act due to tension(string between M1 and pulley.

    Guys put your thoughts here i will thankful for you.
    Last edited by a moderator: Apr 26, 2017
  2. jcsd
  3. Jun 27, 2011 #2
    First off, think about what forces will act on block M2. What force do you think would cause it to accelerate, what force is missing that you think would not cause acceleration? Why?
  4. Jun 27, 2011 #3
    need FBD see it
    this is large image so download it before viewing else it will hard to see what's there.
    thank's for replying. Waiting for other replies.
    Last edited by a moderator: Apr 26, 2017
  5. Jun 27, 2011 #4
    In the first case, the acceleration of M2 is zero because there is no friction between M1 and M2. Thus, the acceleration of M1 will not affect M2.

    In the second case, M2 will accelerate because there is friction between M1 and M2. If M1 accelerates, then the frictional force will cause M2 to accelerate forward. By how much? Depends on the amount of friction. The accelerations of the boxes can be found by applying Newton's Third Law since the frictional forces they exert on each other are equal. Since their masses are not equal, consequently, their accelerations will not equal.
    Last edited by a moderator: Apr 26, 2017
  6. Jun 27, 2011 #5
    why the T (tension) I round in diagram (i put here in last post) make a change ? this tension is in both cases.
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