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Homework Help: Find the tension on the rope

  1. May 24, 2005 #1
    I need to figure this question out. I have to find the tension on the rope (1.14m) after swinging an airplane (.115kg) in the air for 1.49s. Any help?

    I did it like this. I found the velocity (v=d/t) using .82m as the distance (radius) (or should I have used 1.14m instead?). The velocity was .77m/s^2. Then, I found the centripetal force (Fc=mv^2/r) (once again using .82m as "r"). The centripetal force was .08N so I said the tension was .08N.

    Can anyone tell me what I did wrong, and how to do it right? Thanks.
  2. jcsd
  3. May 24, 2005 #2
    How is the radius .82m? Units on velocity are m/s.
    You are correct ins aying the tension is the force, but the rest doesnt really make sense.
  4. May 24, 2005 #3
    I meant .57m for radius. Would that be right, or would I use 1.14 for the distance/radius in the equations?

    How would I find the force then if it doesn't make sense?
  5. May 24, 2005 #4
    Well, the airplane traces a circle around your hand, correct? Whats the radiuso f that circle? The rope, or half hte rope?

    If it makes a revolution in 1.49 seconds, then the circumference of the circle divided by the time gives you the average linear velocity.
  6. May 24, 2005 #5


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    You have not stated the problem well enough for anyone to know for sure if you are doing the right thing, or what you are doing wrong. If 1.49 sec is the time for the plane to go around the circle one time, then you need to say so. If the velocity is constant, it is one sort of problem. If you are doing something to speed the plane up, it is a totally different problem.
  7. May 30, 2005 #6
    Also, did the question specify whether the airplane was moving in a horizontal plane or whether the rope was parallel to the horizontal, because this will affect the value of the radius.
  8. May 30, 2005 #7
    Not the radius, but the force diagram definitely.
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