Billy goes ice skating with his friend Sally. While they are both standing on the ice before skating Billy pushes Sally. What is Billy's (m = 55 kg) velocity after he pushes Sally if Sally has a mass of 45 kg and moves off at 2.5 m/s?

The velocity of Billy is, V = - 2.05 m/s

Explanation:

Given data,

The mass of Sally, m = 45 kg

The mass of Billy, M = 55 kg

Sally's velocity, v = 2.5 m/s

Billy's velocity, V = ?

According to the law of conservation of momentum,

mv + MV = 0

V = - (mv/M)

V = - (45 x 2.5 / 55)

= - 2.05 m/s

Hence, the velocity of Billy is, V = - 2.05 m/s