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Homework Help: A Bouncing Ball- Check

  1. Sep 13, 2008 #1
    1. The problem statement, all variables and given/known data
    A rubber ball bounces. We'd like to understand how the ball bounces. (Do this on paper. Your instructor may ask you to turn in this work.)
    (a) A rubber ball has been dropped and is bouncing off the floor. Draw a motion diagram of the ball during the brief time interval that it is in contact with the floor. Show 4 or 5 frames as the ball compresses, then another 4 or 5 frames as it expands. What is the direction of 'a' during each of these parts of the motion? (b) Draw a picture of the ball in contact with the floor and identify all forces acting on the ball.

    (c) Draw a free-body diagram of the ball during its contact with the ground. Is there a net force acting on the ball? If so, in which direction?

    (d) During contact, is the force of the ground on the ball larger, smaller, or equal to the weight of the ball? Use your answers to parts a-c to explain your reasoning.

    3. The attempt at a solution

    I'm really here to check the answer that I got. I'm new to forces, and am wondering if certain forces are acting at certain times.

    For a), I did 6 frames total. Three compressing the ball and three expanding it. I said that in the first three, the 'a' (which, is the 'a' with a vector symbol above it), is pointed down towards the floor and in the next three frames it points up instead.

    b) Normal force, weight, and spring force are all acting upon the ball.

    c) I said the net force is pointing down, is that right?

    d) The force of the ground is equal to the weight of the ball. How would I use the first three to convey this?

    Thank you!
  2. jcsd
  3. Sep 13, 2008 #2


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    Homework Helper

    Hi Phoenixtears,

    When the ball is slowing down, the acceleration is in the opposite direction as the velocity. When the ball is speeding up, the acceleration is in the same direction as velocity. Do you see what need to be changed here?

    I'm a bit confused here; is there a spring also? (Was there a diagram in the problem that has this?) If it's just a ball bouncing on the floor, then there is just the force from the floor (the normal force) and the weight force.

    How is the net force related to the total acceleration, in terms of directions?

    Do you see how to answer this last one now?
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