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Homework Help: Impulse and Baseball help

  1. Nov 21, 2014 #1
    1. The problem statement, all variables and given/known data
    A(n) 0.142 kg baseball is thrown with a speed
    of 19.5 m/s. It is hit straight back at the
    pitcher with a final speed of 26.6 m/s.
    What is the magnitude of the impulse delivered
    to the ball?
    Answer in units of kg · m/s

    (part 2) Find the average force exerted by the bat on
    the ball if the two are in contact for 0.00109 s.
    Answer in units of N

    2. Relevant equations

    3. The attempt at a solution
    m= 0.142 and vf = 26.6, so mvf = 3.772, vi = 19.5 so mvi = 2.769
    3.772 - 2.769 = 1.0082
    which was wrong of course...
    i think i need to do something with the t in the equation, but there is no t given in the problem

    i also tried it with vi = 0, since velocity would be zero while the ball s on the bat, but that answer (3.772) was wrong as well
  2. jcsd
  3. Nov 21, 2014 #2

    Doc Al

    User Avatar

    Staff: Mentor

    You forgot to take the direction (and thus the sign) of the velocities into account.
  4. Nov 21, 2014 #3

    Is the ball hit in the same direction it is first thrown?
  5. Nov 21, 2014 #4
    oh okay i see, so instead of 3.772 - 2.769, it would be 3.772 + 2.769 = 6.541?
  6. Nov 21, 2014 #5
    it is! thank you so much! for the second part of the question, I would divide the impulse by the time? 6.541/.00109 = 6000.917431 ... that seems a bit large though...
  7. Nov 21, 2014 #6
    oh wait nevermind, this is a baseball being hit off of a bat, those things come off HARD. haha if anything that 6000 number seems a bit on the small side... it is the correct answer though so thank you thank you so much
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