A child in a boat throws a 6.40-kg package out horizontally with a speed of 10.0 m/s,

Question:

A child in a boat throws a 6.40-kg package out horizontally with a speed of 10.0 m/s, Fig 7-31. Calculate the velocity of the boat immediately after, assuming it was initially at rest. The mass of the child is 26.0 kg, and that of the boat is 45.0kg Ignore water resistance.