On an ice skating rink, a girl of mass 50 kg stands stationary, face to face with a boy of mass 80 kg. the children push off of one another, and the boy moves away with a velocity of +3 m/s. what is the final velocity of the girl? –1.9 m/s +1.9 m/s –4.8 m/s +4.8 m/s

Use conservation of momentum.

Initial momentum = 0

Final momentum = momentum of the girl + momentum of the boy = inifial momentum = 0.

Momentum of the girl = - momentum of the boy

mass of the girl * velocity of the girl = - mass of the boy * velocity of the boy

50 kg * velocity of the girl = - 80 kg * 3m/s

=> velocity of the girls = -80 kg * 3m/s / 50 kg = - 4.8 m/s

- 4.8 m/s