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Momentum + Height of rebound

  1. Mar 24, 2007 #1
    I posted all of the questions so you guys can see all the information I have.

    1. The problem statement, all variables and given/known data

    A rubber ball with a mass of 200 g is released from rest from a height of 2.0 m. It falls to the floor, bounces, and rebounds. The graph at right depicts the magnitude of the upward normal force that the floor exerts on the ball at various instants in time. The graph only shows the narrow window of time surrounding the interval when the ball was in contact with the floor.

    a.) How long does it take the ball to fall the 2.0 m to the floor?
    b.) How fast is the ball traveling just before it hits the floor?
    c.) What is its momentum just before hitting the floor (using a coordinate system in which the positive-y axis points in the upward direction)?
    d.) What is the impulse on the ball by the floor during the 10 ms the ball is in contact with the floor?
    e.) What is the impulse on the ball by the earth’s gravitational pull during the same 10 ms?
    f.) By how much does the ball’s momentum change as a result of this 10-ms period?
    g.) How high does the ball rebound?

    2. Relevant equations
    Change of momentum = mass * change of velocity
    V2^2 = 2a*change of position

    3. The attempt at a solution
    Change of velocity = (2.4kg.m/s) / (0.2kg) = 12m/s
    (12m/s)^2 = 2 (9.81m/s2) * change in position
    CHange in position = (144m2/s2) / 2*9.81m/s^2 = 7.34m , which is not correct.
    Also I was able to calculate Acceleration from the impulse on ball by the floor. I am not sure if and/or how I would use that acceleration.
    Anyway I would appreciate any help.
    Last edited: Mar 25, 2007
  2. jcsd
  3. Mar 24, 2007 #2
    I do not see your graph.
  4. Mar 24, 2007 #3
    I attached the graph (it will open as a Word document). For some reason I can't paste it with my message.

    Attached Files:

  5. Mar 25, 2007 #4

    Doc Al

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    Staff: Mentor

    First things first. Answer a, b, & c: those question have nothing to do with your graph; treat the ball as any other falling body. The graph is only relevant for answering d. (For that you'll need the definition of impulse.)
  6. Mar 25, 2007 #5
    Thanks for replying but again I ONLY NEED HELP WITH G, which asks how high the ball will rebound. I already have the correct answers for a-f. I only posted the other questions so you guys would know what information I was given. So if you could look under my orignal post at the attempt to solve the problem and offer some suggestions I would appreiciate it.
  7. Mar 25, 2007 #6

    Doc Al

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    Staff: Mentor

    Next time BE CLEARER. :smile:

    Find the actual speed of the rebounding ball, not its change in speed. (You can use the results of f to find that rebound speed.)
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