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Easy problem that I'm a bit confused about.

  1. Mar 11, 2008 #1
    1. The problem statement, all variables and given/known data

    You have Joe and John playing catch in space. Joe throws the ball to John with a velocity of 7.5 m/s.

    Given Variables
    Joe's mass is 60.9 kg
    John's mass is 79.8kg
    Ball's mass is 6.5kg

    A) Joe's velocity after he throws the ball.
    B) John's velocity after he catches the ball.
    2. Relevant equations

    Sum of the external forces = 0; Psys=0

    For A, I used:
    (Mass of ball+ Mass of Joe) (Velocity of Joe after he throws the ball) + (Mass of ball)(Velocity of Ball) = 0

    I ended up with: Velocity of Joe after he throws the ball = - [(Mass of ball)(Velocity of ball)]/(Mass of Ball + Mass of Joe9)

    After substituting in the numbers, the velocity of Joe is: -.72329 m/s

    For B, I used:

    (Mass of Ball)(Velocity of Ball) = (Mass of John + Mass of Ball)(Velocity of John after he catches the ball)

    The Velocity of John after he catches the ball is: .56489m/s

    Did I set this problem up properly?
    Any suggestions or clarification would be greatly appreciated. Thanks.
  2. jcsd
  3. Mar 11, 2008 #2
    Looks good to me.
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