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Homework Help: Force exerted by a ball to

  1. Mar 18, 2007 #1
    1. The problem statement, all variables and given/known data
    A barefoot field-goal kicker imparts a speed
    of 37 m/s to a football initially at rest.
    If the football has a mass of 0.41 kg and the
    time of contact with the ball is 0.012 s, what
    is the force exerted by the ball on the kicker’s
    Answer in units of N.

    2. Relevant equations

    3. The attempt at a solution
    F= .41 * (37/.012) = 1264.166667 N
    Answer was wrong, wouldn't this obey newtons third law?
    Or am I overlooking something obvious??? Please help!
  2. jcsd
  3. Mar 18, 2007 #2


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    Homework Helper

    You need to think of impulse and momentum for this problem.
  4. Mar 18, 2007 #3
    so would it be,
    impulse = force x time
    1264.16667 N / .012 s = ans?
  5. Mar 18, 2007 #4
    no... why are u trying to solve for impulse when you have to determine force? what are your known and unknown variables? define them... Delta t = 0.012s, massball = .... and so on
  6. Mar 18, 2007 #5
    after defining your variables see if you are famliar with the impulse momentum formula:

    mvf - mvi = momentum (where vf = final velocity and vi = initial velocity)
    impluse = Force*delta t

    impulse = momentum... maybe you can go about solving from there
  7. Mar 18, 2007 #6
    Following your advice and retrying everything I still come up with the same answer that the Force = m ΔV/t
  8. Mar 18, 2007 #7
    hmmm. the answer sounds correct. who told you that the answer was wrong? maybe the answer is supposed to have a negative sign???
  9. Mar 18, 2007 #8


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    Homework Helper

    I get the same answer as the OP. I agree that a negative sign may be needed, since it is equal and opposite to the force of the foot on the ball for Newton's third law.
  10. Mar 18, 2007 #9
    It was just the negative sign! Thanks guys I was killing myself over this
  11. Apr 4, 2009 #10
    how did u solve for it?? anyone?? i have the same problem?
  12. Oct 22, 2009 #11
    Hey i just got it finally, the 37 is added to the 51.5 not subtracted due to it being in the opposite direction. The correct answer is 3750.
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