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Finding velocity after collision if you know mass and height. Help

  1. Oct 5, 2013 #1
    Finding velocity after collision if you know mass and height. Help!!

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

    A 50 gram ball enters a a pendulum with mass 200 g. The pair then swings up to a height of 11 cm.
    find the velocity immediately after the collision? Then find initial velocity of ball before collision.
    2. Relevant equations
    Vf= square root of 2gh.



    3. The attempt at a solution
    Used above equation and got 14.7 which proved incorrect. Any help would be nice! Thanks!!
     
  2. jcsd
  3. Oct 5, 2013 #2

    Doc Al

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    Staff: Mentor

    You're off by a factor of 10, so I suspect a problem with units. Try again!
     
  4. Oct 5, 2013 #3
    Ahh forgot to change 11 cm to meters. My answer of 1.47 proved to be correct! Thanks so much
     
  5. Oct 5, 2013 #4
    So I have 1.47 m/s for my velocity after the collision. How do I find initial velocity of just the ball right before the collision?!
     
  6. Oct 5, 2013 #5
    I tried the equation Vf^2= Vi^2 + 2gh but my answer proved incorrect. The answer I calculated was .07 m/s
     
  7. Oct 5, 2013 #6

    Doc Al

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    Staff: Mentor

    What's conserved during the collision?
     
  8. Oct 5, 2013 #7
    Momentum? Law of conservation of mometum?... I don't have a clue!
     
  9. Oct 5, 2013 #8

    Doc Al

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    Staff: Mentor

    Exactly.

    Sure you do. :wink:
     
  10. Oct 5, 2013 #9
    I used the equation Vf= M1 x Vi / M1 + M2
    1.47 = .05 kg x Vi / .05 + .2 = 7.35.
    My answer was correct!! Thanks so much :)
     
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