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Homework Help: Torque Questions

  1. Jan 14, 2010 #1
    1. The problem statement, all variables and given/known data
    1. Given the mass of Pluto and the sun, and the distance between the two, how would you find how many Earth years are in a Pluto year?

    2. A bird flying over you drops a walnut. If the bird is flying horizontal at an altitude of 23.5m, and the walnut travels a horizontal distance of 12.5m, how fast was the bird flying.

    2. Relevant equations
    1. Centripetal force= mv^2/r???

    2. x= vit +.5at^2???

    3. The attempt at a solution

    I have no idea where to start. Can someone please help lead me down the right path?
  2. jcsd
  3. Jan 14, 2010 #2


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    The gravitational force between the Sun and Pluto provide the centripetal force needed to keep Pluto in orbit. Use this to get the time it takes Pluto to revolve around the Sun.

    Yes you need to use 2. x=x0 vit -(1/2)gt2

    Vertically speaking, what is the initial displacement x0? What is the horizontal range equal to in terms of time and velocity?
  4. Jan 15, 2010 #3
    How does the gravitational force used to find the time?

    I still don't understand number 2, can someone explain it again?
  5. Jan 15, 2010 #4


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    Equate the gravitational force to the centripetal force to find the periodic time T.

    x=x0+vit -(1/2)gt2

    x0 is the initial displacement. If the horizontal velocity is v, then what is the range R(=12.5m) equal to?
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