Question

A rock with a mass of 0.2 kg with a velocity of 5 m/s strikes a stationary 1 kg wooden ball. After the

collision the rock flies back with a velocity of -2 m/s. What is the velocity of the wooden ball after the
collision?
A. -0.4 m/s
B. -1 m/s
C. 0.4 m/s
D. 1.4 m/s

Answer 1

D. 1.4 m/s

Step-by-step explanation:

forward direction is +

back direction is -

Momentum = P = mass x velocity = mv

let v = velocity of ball after collision

Law of Conservation of Momentum: total momentum before the collision must equal the total momentum after the collision

(0.20 kg)(5 m/s) + (1 kg)(0 m/s) = (0.2 kg)(-2 m/s) + (1 kg)v

1 kg·m/s + 0 = -0.4 kg·m/s + (1 kg)v

1 kg·m/s + 0.4 kg·m/s = (1 kg)v rearrange the equation and solve for v

(1 kg)v = 1.4 kg·m/s

v = (1.4 kg·m/s) / (1 kg) = 1.4 m/s