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Homework Help: A high diver jumping off a board (basic force problem)

  1. Sep 18, 2010 #1
    1. The problem statement, all variables and given/known data

    A high diver of mass 50.0 kg jumps off a board 10.0 m above the water. If her downward motion is stopped 2.30 s after she enters the water, what average force did the water exert on her?


    2. Relevant equations

    Fnet=ma
    vf2=v02+2ax

    3. The attempt at a solution

    First I found the final velocity of the diver when she hits the water

    vf2=02+2(9.8)(10)=196

    vf=14 m/s

    Since she is slowed to a stop in 2.3s the average acceleration would be

    14/2.3 = 6.08696

    Knowing acceleration and her mass, we can calculate the force.

    F=50(6.08696)=304.348

    This answer was marked wrong. I'm pretty sure I did everything right. Am I missing something?
     
  2. jcsd
  3. Sep 18, 2010 #2

    kuruman

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    Science Advisor
    Homework Helper
    Gold Member

    Your calculation is correct for the magnitude of the acceleration. Maybe the dumb machine that marked this problem expected a negative sign in front of the acceleration. I say "dumb" because the acceleration is in the "up" direction which is conventionally positive. You may have to ask your teacher for a clarification of this point.
     
  4. Sep 19, 2010 #3
    Thanks for your input, I'll be sure to ask my professor about this problem.
     
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