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Homework Help: Vertical pendulum, mass of object

  1. Oct 1, 2006 #1
    Hi. Consider an object attached to the end of the string that is whirled vertically in a circle of radius r. When it is @ degrees from the horizontal, it has the speed v and the tension in the string is T. What is the mass of the object?

    The picture shows that the object is in the first quadrant travelling clockwise.

    What I've done so far is:

    T + cos @ mg = m v^2 / r

    After plugging in the values given, I've failed to come up with the correct answer. What am I doing wrong? Thank you.
  2. jcsd
  3. Oct 1, 2006 #2
    I had the cosine and sine messed up; it should be:

    T + sin @ m g = m v^2 / r
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