# Billiard ball collision at right angle

#### Brite

1. Homework Statement
Two billiard balls of equal mass move at right angles and meet at the origin of an xy coordinate system. Ball A is moving upward along the y axis at 2.0 m/s and ball B is moving to the right along the x axis with speed 3.7 m/s. After the collision (elastic), ball B is moving along the positive y axis. What is the final direction of ball A and what are their two speeds?

2. Homework Equations
mAvA + mBvB = mav'A + mBv'B
1/2mAvA2 + 1/2mBvB2 = 1/2mAv'A2 + 1/2mBv'B2

3. The Attempt at a Solution
I know that because this is an elastic collision, momentum and kinetic energy are conserved. I think it's just that the two balls start on different axes is what's throwing me off.

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#### LowlyPion

Homework Helper
1. Homework Statement
Two billiard balls of equal mass move at right angles and meet at the origin of an xy coordinate system. Ball A is moving upward along the y axis at 2.0 m/s and ball B is moving to the right along the x axis with speed 3.7 m/s. After the collision (elastic), ball B is moving along the positive y axis. What is the final direction of ball A and what are their two speeds?

2. Homework Equations
mAvA + mBvB = mav'A + mBv'B
1/2mAvA2 + 1/2mBvB2 = 1/2mAv'A2 + 1/2mBv'B2

3. The Attempt at a Solution
I know that because this is an elastic collision, momentum and kinetic energy are conserved. I think it's just that the two balls start on different axes is what's throwing me off.
Welcome to PF.

Indeed the 2 dimensions do make a difference. You will want to treat them separately.

Momentum in x is conserved
Momentum in y is conserved
KE is conserved.

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