Running at 2.0 m/s a 45.0 kg person collides with a 90.0 kg person who is traveling at 7.0 m/s in the other direction. Upon collision, the 90 kg person continues to travel forward at 1.0 m/s. How fast is the 45 kg person knocked backwards?

Answer 1

Given: m/s.
M 1 = 45 kg, V1 = 2 m/s.
M2 = 90 kg, V2 = -7 m/s.
V3 = Velocity of M1 after collision.
V4 = -1 m/s = Velocity of M2 after collision.

Momentum before = Momentum after
M1*V1 + M2*V2 = M1*V3 + M2*V4.
45*2 + 90*(-7) = 45V3 + 90*(-1),
90 - 630 = 45V3 - 90,
-450 = 45V3,
V3 = -10 m/s.