A man wearing a bullet-proof 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 then the velocity of the man?
m - Mass of bullet
= 0.02 kg
M - Mass of man
= 80 kg
u - Initial velocity of bullet
= 400 m/s
U - Initial velocity of man
= 0 m/s
v - Final velocity of bullet
= 0 m/s
V - Final velocity of man
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
V = 0.1 m/s
Therefore, the man moves with a velocity of 0.1 m/s