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Flying Kite

  1. Jul 16, 2009 #1
    1. The problem statement, all variables and given/known data
    You are a judge in a children's kite-flying contest, and two children will win prizes for the kites that pull most strongly and least strongly on their strings. To measure string tensions, you borrow a weight hanger, some slotted weights, and a protractor from your physics teacher, and use the following protocol. Wait for a child to get her kite well controlled, hook the hanger onto the kite string about 30 cm from her hand, pile on weight until that section of string is horizontal, record the mass required, and record the angle between the horizontal and the string running up to the kite.

    a) Explain how this method works. As you construct your explanation, imagine that the children's parents ask you about your method, that they might make false assumptions about your ability without concrete evidence, and that your explanation is an opportunity to give them confidence in your evaluation technique.

    b) Find the string tension if the mass is 132 g and the angle of the kite string is 46.3 degrees.

    3. The attempt at a solution
    My thought on this was that there there are three forces: the two tensions and the force of the mass. Say T2=The tension on the left of the masses and T1=The tension on the right of the masses. Since the masses are in equilibrium F=0. In the x component T2=T1Cosθ. In the y component T1Sinθ=mg. Then I solved for T1 and T2. T1=mg/(Sinθ) and T2=mg/(Tanθ). Now if I knew which tension we were measuring, that would be great. I think we are measuring T2 so we want to find when mg/(Tanθ) is the max or min. For Tmax we want θ to be close as possible to 0 and m high. For Tmin we want a small m and θ as close to 90 as possible. Is this a good explanation? As for part (b) I think if it is asking for T2, then I got it. THANKS FOR YOUR TIME.
  2. jcsd
  3. Jul 17, 2009 #2
    i guess you got it right
  4. Jul 17, 2009 #3
    Ok thanks but why is it asking me for the tension in the T2 and not T1?
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