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Birds Colliding mid-air, Conservation of Momentum

  1. Oct 20, 2013 #1
    1. The problem statement, all variables and given/known data
    To protect their young in the nest, peregrine falcons will fly into birds of prey (such as ravens) at high speed. In one such episode, a 560g falcon flying at 19.0m/s hit a 1.60kg raven flying at 9.0m/s . The falcon hit the raven at right angles to its original path and bounced back at 5.0m/s . (These figures were estimated by the author as he watched this attack occur in northern New Mexico.)

    By what angle did the falcon change the raven's direction of motion?

    2. Relevant equations

    3. The attempt at a solution
    I set the falcon to be the y direction, and the raven to be the x direction. Using conservation of momentum, I came up with
    (19 m/s)(0.56 kg) = (-5 m/s)(0.56 kg) + (1.6 kg) (vy) to find the y component of the end velocity of the raven. I got 6.825 m/s as the answer
    (9 m/s)(1.6 kg) = (1.6 kg)(vx) to find the x component of the end velocity of the raven. I got 9 m/s as the answer.
    Using the arc tangent of those two numbers, I got 37.1745483°, rounded to two significant figures, that is 37°, however this answer is incorrect. I'm not sure what I'm doing wrong, could someone please help?
  2. jcsd
  3. Oct 20, 2013 #2


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    Momentum in x and y are separately conserved. So if the falcon (moving in y) bounces back in the same direction (y) then it only changes the momentum of the raven in the y axis. The momentum of the raven in the x axis is unchanged. I think!
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