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

  • Thread starter astru025
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  • #1
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Finding velocity after collision if you know mass and height. Help!!

Homework Statement



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.

Homework Equations


Vf= square root of 2gh.



The Attempt at a Solution


Used above equation and got 14.7 which proved incorrect. Any help would be nice! Thanks!!
 

Answers and Replies

  • #2
Doc Al
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Used above equation and got 14.7 which proved incorrect.
You're off by a factor of 10, so I suspect a problem with units. Try again!
 
  • #3
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Ahh forgot to change 11 cm to meters. My answer of 1.47 proved to be correct! Thanks so much
 
  • #4
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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?!
 
  • #5
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I tried the equation Vf^2= Vi^2 + 2gh but my answer proved incorrect. The answer I calculated was .07 m/s
 
  • #6
Doc Al
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44,892
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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?!
What's conserved during the collision?
 
  • #7
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Momentum? Law of conservation of mometum?... I don't have a clue!
 
  • #8
Doc Al
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44,892
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Momentum? Law of conservation of mometum?
Exactly.

... I don't have a clue!
Sure you do. :wink:
 
  • #9
163
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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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