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Tension and Weight of Ball (Mg)

  1. Feb 22, 2010 #1
    1. The problem statement, all variables and given/known data

    A wrecking ball of mass M is suspended by a thin cable (of negligible mass). The ball's position is recorded by a flash camera three times at intervals of 95 ms. For each of the sequences illustrated below, the tension remains constant. Indicate whether the tension in the cable, T, is Greater than, Less than, or Equal to the weight of the ball, Mg, or whether one Cannot tell.

    2. The attempt at a solution

    I don't even know how to decipher what the pictures mean.

    But I did try:

    1. Greater than
    Equal to
    Greater than
    Cannot tell
    Equal to
    Equal to
    Cannot tell
    Equal to
    Less than

    Attached Files:

  2. jcsd
  3. Feb 22, 2010 #2
    So we start off with two different forces in opposing direction and we have to compare them. There can be an equilibrium of forces with a net force of zero but with constant velocity. (Diagram 5 and 8)

    And there can be static equilibrium where the net force is zero and the box is not moving. (Diagram 2)

    Everything else we have to look at the position of the box from one image to another to determine the change in velocity.
    Just because a box is moving up doesn't mean it has a net acceleration upwards. For example, in Diagram 3 the box is moving up but it is slowing down and therefore has a net acceleration downward (so the downward force is greater than the tension).

    I'm not sure about Diagrams 9. It doesn't make sense.
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