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Determining the time of a collision

  1. Jan 22, 2013 #1
    1. The problem statement, all variables and given/known data
    A 473-gram baseball traveling at 37 m/s is hit directly back at the pitcher with a speed of 45 m/s. If the force of contact between the bat and the ball is 3800 Newtons, how long is the bat in contact with the ball?

    2. Relevant equations
    F= dp/dt

    3. The attempt at a solution
    t=(.473)(8)/(3800) ---> converted 473g into kg because newtons are kg*m/s2
    t=.000996 s

    But that's not the right answer. I've also tried not converted g->kg and that doesn't work either, so obviously there's something else I'm doing wrong, but I just don't know what it is.
  2. jcsd
  3. Jan 22, 2013 #2


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    The difference in velocities between 37m/s towards the bat and 45m/s away from the bat is 82m/s. You have to consider the sign of the velocities.
  4. Jan 22, 2013 #3
    Wow, that completely went over my head... now I feel really stupid, haha. Thanks for pointing that out, sorry for the waste of a post.
  5. Jan 22, 2013 #4


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    Don't feel sorry. That's what the forum is for. If you get it the post is hardly wasted.
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