# Momentum elastic colliion in 2D

• euphoriax

## Homework Statement

A hockey player of mass 8.0x10 kg was skating at a velocity of 7.5 m/s [E] when he accidentally hit a linesman who was just standing on the ice. The mass of the linesma is 9.0x10 kg and his velocity after the collision was 3.0 m/s [N30°E].
a) find the velocity of the hockey player after the collision
b) find the kinetic energy lost during the collision

p=p'
p=mv
0.5mv2 = v

## The Attempt at a Solution

since momentum is conserved: (horizontal E (+) direction)
Pb=Pa
mAvA + mBvB= mBvB' + mAvA'
80kg(7.5m/s) + 0kgm/s = 90cos 30° + 80vAcosθ
600-90cos30°= 80vAcosθ
(600-90cos30°)/80 = vAcosθ
6.5 m/s = vAcosθ

I'm not really sure about what to do next, do i just continue with finding the vAsinθ for the same direction and then do the same things for the vertical direction? Are there any other solid steps that i need to know in order to solve a 2D momentum question?
Thanks

What you have done is correct for the momentum in the E direction.
You now need to do a similar thing for the momentum in the N direction for the linesman and the equivalent momentum in the S direction for the player.
This will involve the Sine30 and the Sine∅