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Average acceleration of impact of ball.

  1. Aug 16, 2015 #1
    A ball travels vertically downwards until it hits a concrete floor with speed 16.1-m/s. It then bounces vertically upwards at 3.4-m/s. Examination of a high speed video shows that the collision took 1.1-ms. Considering just the collision, what is the magnitude of the average acceleration?

    b)
    For some balls, the acceleration of the center of the ball, in a collision like this, is fairly constant. So, assuming constant acceleration, what is the maximum deformation of the ball? (i.e. what is the maximum distance that the center of the ball travels downwards?)

    I believe this should be delta V/time, however the answer comes out wrong.
    I have 3 attempts at the question and each wrong answer 33.3% of the mark is lost so I'm scared to attempt the question again without being certain.

    There is also part b) which I have 0 idea how to even start.

    So what I have done is:

    (3.4+16.1)/0.0011 = 19500 (edit: divided by 0.001, should be 17727.273. Is this correct?)

    0.0011 for time as it was given in milliseconds

    As for direction it asks for magnitude so it should be irrelevant

    I also found this thread and it seems like I'm doing it right so I'm really confused.
    https://www.physicsforums.com/threa...e-acceleration-during-point-of-impact.797568/

    Any ideas what i'm doing wrong?

    Thanks,
    Danny

     
  2. jcsd
  3. Aug 16, 2015 #2

    haruspex

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    Assuming the answer is supposed to be in m/s2, your answer looks right to me. Don't quote an unjustifiable number of significant digits.
     
  4. Aug 16, 2015 #3
    Thanks, yeh was correct .

    Any ideas on part b? Have 0 idea where to even start.
     
  5. Aug 16, 2015 #4

    haruspex

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    What equations do you know related to constant acceleration in one dimension? SUVAT?
     
  6. Aug 16, 2015 #5
    s = ut + ½ at^2

    Am i meant to use this equation?
    If so why? I don't quite understand the question.
     
  7. Aug 16, 2015 #6

    haruspex

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    That is one of five standard SUVAT equations. There are five variables, s, u, v, a, t, each equation involves four of them. You need to pick the equation which involves the three whose value you know and the one which you are trying to find.
    A complication here is that they have given you inconsistent information! If the acceleration were truly constant through the whole process then it would rebound with the same speed. (Alternatively, it would lose contact with the ground before reaching the height at which it originally made contact, because the balls is still deformed and not exapnding fast enough.)
    You could just consider the downward movement. You know the initial speed, the final speed and the time.
     
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