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Homework Help: Linear speed/how many revolutions are made?

  1. Dec 4, 2011 #1
    1. The problem statement, all variables and given/known data
    a quarter back throws a pass that is a perfect spiral, and the spins at 7.7 rev/s. the linear speed is 19 m/s and at an angle 55. if the ball is caught the same height it is thrown, how many rev. has the ball made while in the air?

    2. Relevant equations
    ω^2 = ωnot^2 + 2(alpha) (theta)

    3. The attempt at a solution
    ω^2= (48rad/s)^2+ 2(19m/s)(55) = 66.56 rad/2pi= 104.56 rev
    this answer is not right...i think that alpha is something else like a/r but i dont have r...thanks for help
    Last edited: Dec 4, 2011
  2. jcsd
  3. Dec 4, 2011 #2


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    Gold Member

    You seem to be confusing two independent motions: the translational motion of the ball through the air, and the ball's spin. These two are separate and unrelated (i.e. they do not influence each other). So, you basically have two problems to solve:

    1. Solve the projectile motion problem to figure out how long the ball stays in the air (given the initial speed and launch angle).

    2. Figure out how many spins would have occurred during the time spent in the air computed in part 1.
  4. Dec 4, 2011 #3
    ok ill try that thank you!
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