In the movies a person hit by a bullet goes flying back from the momentum of the bullet (typically into a plate-glass window),find the final speed of a 84-kg man just after he is hit by a 44magnum bullet of mass 16 g traveling at a speed of 470 m/s.
A)0.090 m/s
B)0.25 m/s
C)5.6 m/s
D)7.5 m/s

Question

Quizplus · Accepted Answer

To find the final speed of the man just after being hit by the bullet, we use the principle of conservation of momentum. The total momentum before the collision (bullet + man) must equal the total momentum after the collision.Initial momentum of the bullet = mass of bullet * velocity of bullet = 0.016 kg * 470 m/s = 7.52 kg·m/s. The man is initially stationary, so his initial momentum is 0.The total initial momentum = momentum of bullet + momentum of man = 7.52 kg·m/s + 0 = 7.52 kg·m/s.After the bullet hits the man, their combined mass = mass of man + mass of bullet = 84 kg + 0.016 kg = 84.016 kg.Let $v$ be their final velocity. By conservation of momentum, the total initial momentum = total final momentum.$$7.52 = 84.016 \cdot v$$Solving for $v$, we get:$$v = \frac{7.52}{84.016} \approx 0.0895 \, \text{m/s}$$Rounded to three significant figures, the final speed is 0.090 m/s.

In the Movies a Person Hit by a Bullet Goes