# A man wearing a bulletproof vest stands still on roller skates. The total mass is 80 kg. A bullet of mass 20 grams is fired at 400 m/s. It is stopped by the vest and falls to the ground. What is the velocity of the man?

##### 1 Answer

Nov 18, 2015

#### Explanation:

Using conservation of momentum,

#"initial momentum " = " final momentum"#

#m * u + M * U = m * v + M * V#

#0.02 * 400 + 80 * 0 = 0.02 * 0 + 80 * V#

#8 = 80 * V implies V = "0.1 m/s"#

Therefore, the man moves with a velocity of