# Homework Help: Final question of the day! help finding impulse of two billiard balls

1. Oct 26, 2007

### pebbles

1. The problem statement, all variables and given/known data
A billiard ball going 4 m/s collides with a stationary ball of equal size cause the second ball to move at an angle of 35 degrees at speed of 2.5 m/s
--mass=.3 kg
What impulse (magnitude and direction) did second ball receive? What about the first ball?
What is the final velocity (magnitude and direction) of the frist ball?

2. Relevant equations
impulse=kg * m/s
final velocity...?

3. The attempt at a solution
Impulse of second ball=.3*2.5= .75 kg*m/s
Impulse of first ball=.3*4=1.2 kg*m/s
Those right? How do I calculate the direction....?

2. Oct 26, 2007

### TMM

You can make life a little easier for yourself by keeping the vector definitions of the initial momenta. Then when you finish, direction will be incorporated into your answer, you'd just need to find the magnitude.

3. Oct 26, 2007

### Shooting Star

Billiard balls are assumed to be perfectly elastic.

What quantities are conserved in elastic collisions?

4. Oct 26, 2007

### pebbles

shooting star-kinetic and momenta

5. Oct 26, 2007

### Shooting Star

Then why don't you equate the initial and final energies and momenta rpty?

Resolve the final momenta in the two directions along and perp to the initial direction of the first ball.