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Homework Help: Impulse and average force of baseball

  1. Nov 10, 2007 #1
    i dont understand wat im doing wrong here is my problem
    Choose the positive direction to be
    from the pitcher to the plate (some answers
    may be negative).
    A pitcher throws a 0.13 kg baseball so that
    it crosses home plate horizontally with a speed
    of 31 m/s. It is hit straight back at the pitcher
    with a final speed of 28 m/s.
    What is the impulse delivered to the ball?
    Answer in units of kg m/s
    Find the average force exerted by the bat on
    the ball if the two are in contact for 0.0011 s.
    Answer in units of N

    ok here is my work
    then for average force i have
    but i change my signs to positive right?? either way my answer is wrong help please
  2. jcsd
  3. Nov 10, 2007 #2


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    Science Advisor
    Homework Helper
    Gold Member

    the problem asks you to consider pitcher to batter as the positive direction, thus, batter to pitcher is the negative direction. What is the direction of vf?
    once you correct the value of impulse, your force will be correct and it will ahve a minus sign associated with it. What does the minus sign indicate about the direction of the force of the bat on the ball?
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