A boy with a mass of 35.4 kg comes running up behind his stationary father, whose mass is 105.3 kg. If the boy’s velocity before the collision is 8.20 m/s eastward, and his father’s velocity after the collision is 3.10 m/s eastward, find the boy’s velocity after the collision, both magnitude and direction.
Answer: 1.02 m/s, westward
momentum is conserved, so the sum of boy's and father's momentum must be unchanged:
(35.4)(8.20)+(105.3)(0) = (35.4)v + (105.3)(3.10)
v = -1.02
which is westward