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Homework Help: Questions about circular motion/ centripetal acceleration/force

  1. Mar 30, 2008 #1
    1. The problem statement, all variables and given/known data
    a 20 kg ball attached to a string is moving in constant circular motion. if theta= 10 degrees and the radius of its circular path is 0.5 m, what is the ball's velocity?

    2. Relevant equations

    3. The attempt at a solution

    As far as I got was F(net)=F(centripetal), then I was lost
  2. jcsd
  3. Mar 30, 2008 #2
    What forces are on your ball? (draw it and then an fbd)
  4. Mar 30, 2008 #3
    Oh! The teacher told the class that there are only two forces acting on the ball. There is F(centripetal) and there is F(gravity) which is 196 N I got that from the information. What is an fbd?
  5. Mar 30, 2008 #4
    Free Body Diagram~ it's where you draw the object (or usually just a dot to represent it) and use arrows on it to represent the forces.
    Also, the centriptial force is not a new force (the name is misleading), its the net force of a circular motion problem. Certain forces on the object (like weight, etc) cause the circular motion, which results in an overall net force that makes the object go in a circle. (circular overall net force = centripital force). So what forces make your object go in a circle?
  6. Mar 30, 2008 #5
    Yes, there's a weight component, and there's a centripetal force, but there's also tension. How can you relate these three?
  7. Mar 31, 2008 #6


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    It appears the string is at an angle...while another force is perpendicular to the object... If the object doesn't move up or down, doesn't that mean that something is balancing out the force? If so, how does a Force at an angle balance it out? (think vectors)
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