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Homework Help: What is the speed of the 8-ball after the collision?

  1. Oct 21, 2014 #1

    1. In a pool game, the cue ball, which has an initial speed of 1.3 m/s, makes an elastic collision with the 8-ball, which is initially at rest. After the collision, the 8-ball moves at an angle theta = 33.2o with respect to the original direction of the cue ball, as shown in the figure. Assume the pool table is frictionless and the masses of the cue ball and the 8-ball are equal. What is the speed of the 8-ball after the collision?


    2. Mgh + W = 1/2mv^2

    3. I was easily able to get that phi was 56.8 deg because of the 90 deg angle. Now I am lost at how to find the velocity of the 8 ball without the velocity of the cue ball???
  2. jcsd
  3. Oct 21, 2014 #2


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    Hello White and welcome to PF :-)

    Your collection of relevant equations needs revision and extension. Mgh and W are unlikely to play a role in this drama....
  4. Oct 28, 2014 #3


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    Conservation of momentum and energy are most important. But "Mgh" is irrelevant here. It is the potential energy of a mass M at height h, but there is no "height" here.
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