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Collision and IMpulse

  1. Jul 8, 2008 #1
    1. The problem statement, all variables and given/known data
    A 300g ball with a speed v of 6.0m/s strikes a wall at an angle theta of 30 degrees and then rebounds with the same speed and angle. It is in contact with the wall for 10ms. In unit-vector notation, what are (a) the impulse on the ball from the wall and (b) the average force on the wall from the ball?

    http://ready2goxtr.googlepages.com/problem936.jpg


    2. Relevant equations
    Pi = Pf

    Delta (P) = I
    P = mv
    <v being a vector>

    Favg = I / (delta T)


    3. The attempt at a solution

    m = .3kg v = 6m/s theta = 30 degrees t = 10ms = .01s

    a) Pi = PF

    Pi = .3kg(Vcos(-30) i + Vsin(-30) j) = .26 kg * m/s i - 3 kg * m/s j

    Pf = .3kg(Vcos(30) i + Vsin(30) j) = .26 kg * m/s i + 3 kg * m/s j

    I = Delta (P) I = PF - PI

    PF - PI = 6 kg * m/s j


    b) I = sqrt(a^2 + b^2)
    6kg * m/s / .01s = 600 N



    I know i did it wrong. And thank you ahead of time.
     
  2. jcsd
  3. Jul 8, 2008 #2

    Doc Al

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    Staff: Mentor

    Double check your arithmetic.
     
  4. Jul 8, 2008 #3
    whats wrong with it? Sorry if im a bit slow, all the chemotherapy i had last year sorta slowed me down i think.
     
  5. Jul 8, 2008 #4

    Doc Al

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    Staff: Mentor

    For example: .3*6*sin(30) = ?
     
  6. Jul 8, 2008 #5
    Oh Duh me. 0.9 but still, I highly doubt that I = 1.8 kg * m/s J
     
  7. Jul 8, 2008 #6
    well in that case I = 1.9 kg * m/s J and Favg = 180 N
     
  8. Jul 8, 2008 #7
    Okay so that must be right answer then?
     
  9. Jul 8, 2008 #8

    Doc Al

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    Staff: Mentor

    Sounds good to me. Express your answers using unit vectors.
     
  10. Jul 8, 2008 #9
    Do i need to open up a new post for a new question?
     
  11. Jul 8, 2008 #10

    Doc Al

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    Staff: Mentor

    In general: If it's a new problem, use a new thread. If it's a followup question on the same problem, ask it here.
     
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