Billiard glancing collision

1. Oct 18, 2009

tienlam

In the arrangement of the figure, Billiard ball 1 moving at a speed of 2.0 m/s undergoes a glancing collision with identical billiard ball 2 that is at rest. After the collision, ball 2 moves at speed 0.9 m/s, at an angle of θ2 = 55°.

(a) What is the magnitude of the velocity of ball 1 after the collision?
(b) What is it's direction?
(c) Can the collision be inelastic, given these data?

I'm not sure but im assuming that the masses are equal for each ball.
Using momentum conservation for each x y dimension i got:

An attempt at solution:

X direction:
m = mass of balls
V1fx = final velocity of ball 1 in x direction

(2.0m/s)(m) = (m)(0.9m/s)(cos55) + (m)(V1fx)
cancelling out m i get that V1fx = 1.98 m/s

Y direction:
0 = (m)(0.9)sin55 + (m)(V1fy)
V1fy = -0.89 m/s

V1f^2 = 0.89^2 + 1.98^2,

V1f = 2.175 m/s

tanθ1 = 0.89/1.98 θ1 = 0.422

I'm not sure what im doing wrong.

2. Oct 18, 2009

tienlam

Nevermind, i've found what the problem was.