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Homework Help: AP problem

  1. Apr 7, 2007 #1
    I need with a problem....A 0.10 kilogram solid rubber ball is attached to the end of an 0.0 meter length of light thread. The ball is swung in a vertical circle. point P, the lowest point of the circle, is 0.20 meter above the floor. The speed of the ball at the top of the circle is 6.0 meters per second, and the total energy is kept constant.
    a)Determine the total energy of the ball, using the floor as the zero point for gravitational potential energy.

    b)Determine the speed of the ball at point P, the lowest point of the circle

    c)Determine the tension of the thread at...
    i. the top of the circle
    ii. the bottom of the circle

    The ball only reaches the top of the circle once before the thread breaks when the bal is at the lowest point of the circle.
    d)Determine the horizontal distance that the ball travels before hitting the floor

    I'm not sure where to begin.

    If anyone can help me it would be great!!
  2. jcsd
  3. Apr 7, 2007 #2


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    Homework Helper

    The length of the thread is 0.0 m???

    You must show some work in the Homework forums. Can you think of anything useful in approaching this problem (relevant equations, etc)?
    Last edited: Apr 7, 2007
  4. Apr 7, 2007 #3
    sry.im new to all of this stuff. the length of thread is 0.80 meters. well for part A i was Thinking PE=m*g*h because it said Potential energy. I get . Part B i think you do .5*m*v^2 = mgh and solve for the velocity. The for C the tension at the top is 0 or (m*g), not to sure on that one. D i can figure out using a kinematic equation
  5. Apr 7, 2007 #4


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    For a), you do need to consider the gravitational potential energy. But the ball is moving, so you need to consider the kinetic energy as well to get the total energy.

    For b), since the energy remains constant, the energy at the top of the circle must equal the energy at the bottom of the circle. Since the ball is now closer to the floor, the relation between the potential and kinetic energies change. So just write out the terms for each.

    For c), use the idea of a centripetal force with Newton's second law.

    For d), yes, you can use kinematics to find the distance.
  6. Apr 7, 2007 #5
    thank you very much. that was very helpful
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