Question

An 85.00 kg man playing hockey catches a puck moving at 20 m/s. The man is initially at rest. The man and the puck move together after the collision. The puck's mass is 0.16 kg. What is the final velocity?

Answer 1

`v=0.04ms^(-1)` to 2dp

Explanation:

We want to use the law of conservation of momentum. What this means is that the total momentum of our man-puck system is the same value before and after the collision in the absence of dissipative forces like friction, which we are assuming is not present.

Total momentum before = Total momentum after

We will denote velocity before as `u` and velocity after as `v`

`M_(man)u_(man) + M_(puck)u_(puck) = (M_(man) + M_(puck))v`

But `u_(man) = 0` so:

`v = (M_(puck)u_(puck))/(M_(man) + M_(puck))`

Velocity is a vector so it's direction matters, but since the direction will be the same as the direction the puck was going in originally it's not so important.

`v = (0.16*20)/(85.00+0.16) = 0.04ms^(-1)` to 2dp