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Homework Help: Three Blocks Connected Concepts

  1. Jun 11, 2015 #1
    Unsure what or which answers are incorrect.

    1. The problem statement, all variables and given/known data

    In the figure below, assume that the pulleys are massless and frictionless.
    **Attached File**
    The masses of the blocks are Ma=1.50 kg, Mb=4.00 kg, Mc=6.00 kg, and there is friction between the horizontal plane and Mc, (μk≠0). Mc is observed to travel at a constant velocity.

    True, False, Greater than, Less Than, or Equal to
    Tx is .... Ty
    Mc is moving to the right
    Ma*g is .... Tz.
    The magnitude of the total force on Mc is .... 0
    Mb accelerates downward
    Tz is .... Ty

    2. Relevant equations

    3. The attempt at a solution
    I've got it answered as.
    Tx is EQUAL to Ty
    Mc is moving to the right TRUE
    Ma*g is LESS THAN Tz.
    The magnitude of the total force on Mc is EQUAL TO 0
    Mb accelerates downward TRUE
    Tz is LESS THAN Ty

    Attached Files:

  2. jcsd
  3. Jun 11, 2015 #2


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    Some of these are incorrect.

    "Mc is observed to travel at a constant velocity"

    What does this imply about the motion of Ma and Mb?
    And what does the mean about the sum of the forces on Ma & Mb?
  4. Jun 11, 2015 #3
    The motion as in Ma will rise and Mb will fall? Also meaning the force on Mb is greater than Ma?
  5. Jun 11, 2015 #4


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    Science Advisor

    The acceleration of Mc is zero, what, then, is the acceleration of Ma and Mb?
  6. Jun 11, 2015 #5
    Last edited: Jun 11, 2015
  7. Jun 11, 2015 #6
    Honestly I just need the answer, I'm running out of time.
  8. Jun 11, 2015 #7


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    Science Advisor

    Imagine a truck towing a trailer, can the truck go at constant velocity and the trailer be accelerating? Can the trailer go faster or slower than the truck?

    Masses A,B & C are connected. Unless otherwise stated always assume that string does not stretch or go slack. In other words, the velocity and acceleration of all three blocks is equal.
  9. Jun 11, 2015 #8
    Yes, I'm still very confused which answer you offering hints for which are incorrect
  10. Jun 11, 2015 #9
    • This is an unacceptable response on Physics Forums.
    Well you were no help....
  11. Jun 11, 2015 #10


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    Please see the rules:

    Particularly these parts:
    • Full solutions on a homework problem should never be given. Only hints and explanations are allowed.

    • Giving Full Answers:
      On helping with questions: Any and all assistance given to homework assignments or textbook style exercises should be given only after the questioner has shown some effort in solving the problem. If no attempt is made then the questioner should be asked to provide one before any assistance is given. Under no circumstances should complete solutions be provided to a questioner, whether or not an attempt has been made.

    Also, it's generally considered bad manners to edit/remove posts. It makes the thread harder for others to follow (and less likely to help..).
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