- #1

mdergance3

- 13

- 0

If I have a cue ball moving to the right with velocity of 4 m/s and it hits another stationary cue ball with equal mass. The first cue ball is deflected at a velocity of 1.5 m/s @ 45° in the north east direction. What is the velocity and direction of the 2nd cue ball.

I apply conservation of linear momentum, I'm going to negate the masses since they are equal.

4 = 1.5*cos45 + v_x

where v_x is the x component of the 2nd cue ball

v_x = 2.94 m/s

Now the y direction:

1.5*sin45 = -v_y

v_y = 1.06m/s

magnitude of 2nd cue ball's veloctiy = sqrt(1.06^2 + 2.94^2) = 3.125

Now conservation of energy:

.5*m*4^2 = .5*m*3.125^2 + .5*m*1.5^2

16 = 12.01 <-- this is not true, why? what am I doing wrong?