# Homework Help: Calculating angle of ball after collision

1. Nov 27, 2015

### Felicity Wang

1. The problem statement, all variables and given/known data
The white ball in the figure has a speed of 1.81 m/s and the yellow ball is at rest prior to an elastic glancing collision. After the collision the white ball has a speed of 1.37 m/s. To the nearest tenth of a degree, measured counterclockwise from east, what angle does it scatter at if the yellow ball is scattered at 280degrees?

2. Relevant equations
mv1=mv1'sin(@)+mv2'sin(@)

3. The attempt at a solution
(2kg x 1.81m/s) = (2kg x 1.37) sin(@) +(1kg) v2' sin(280)

v2':
1/2mv1^2 = 1/2mv1'^2 + 1/2mv2'^2
v2'= 1.67m/s

The answer is 37 degrees but I am not sure how to progress from here.

2. Nov 27, 2015

### JeremyG

I would recommend drawing a free body diagram of the two balls as well as vector triangles to get a better grasp of the situation here. For one, do not apply the equations blindly. The very first step here:
is meant to be a statement of Conservation of Linear Momentum in the horizontal direction, yes?

What then, is the direction of the momentum vector you are considering when you use sin(@)?

3. Nov 27, 2015