Elastic collision in 2-d.

  • Thread starter LTZach
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  • #1
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Homework Statement


Consider an elastic collision (ignoring friction and rotational motion). A queue ball initially moving at 2.9 m/s strikes a stationary eight ball of the same size and mass. After the collision, the queue ball’s final speed is 1 m/s. Find the queue ball’s angle with respect to its original line of motion.
Answer in units of ◦.



Homework Equations


I can't seem to figure out how you're supposed to get an angle for this, if none is given.


The Attempt at a Solution


in 1-d the equation would be something like m1v1+m2v2=(m1+m2)*V. In 2-d, I assume you need a trig function, but how is that useful with no given angle?
 

Answers and Replies

  • #2
tiny-tim
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Welcome to PF!

Hi LTZach ! Welcome to PF! :wink:
Consider an elastic collision (ignoring friction and rotational motion). A queue ball initially moving at 2.9 m/s strikes a stationary eight ball of the same size and mass. After the collision, the queue ball’s final speed is 1 m/s. Find the queue ball’s angle with respect to its original line of motion.
Answer in units of ◦.

how is that useful with no given angle?
(btw, it's a cue ball! :wink:)

Call the angle θ, and find three equations, for momentum in the x and y directions, and for energy.

What do you get? :smile:
 

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