Momentum of colliding billard balls

  • #1

Homework Statement



A white billiard ball with mass mw = 1.43 kg is moving directly to the right with a speed of v = 3.29 m/s and collides elastically with a black billiard ball with the same mass mb = 1.43 kg that is initially at rest. The two collide elastically and the white ball ends up moving at an angle above the horizontal of θw = 21° and the black ball ends up moving at an angle below the horizontal of θb = 69°.
http://smartphysics.com/images/content/mechanics/ch12/billiardballsnew2.png [Broken]

I need to find the final speeds of the balls.


Homework Equations



Conservation of momentum

The Attempt at a Solution




What I tried already was having initial momentum equal to final momentum. And then splitting it into x and y components and solving for the unknown velocities and got 1.4 for the black one and 3.66 for the white one. I'm not sure where I went wrong. Please help.

Here is some of my work:
Since masses cancel out, I have
for X: 3.92 + 0 = Vwcos21 + Vbcos69
for y: 0 = Vwsin21 - Vbsin69
Then solved for Vb, which I got 1.4, but it's wrong.
 
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Answers and Replies

  • #2
vela
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Your method is fine. You just swapped two digits in the initial velocity.
 

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