Please help me!

Question

A child in a boat throws a 5.65 kg package out horizontally with a speed of 10.0 m/s.  



Calculate the velocity of the boat immediately after, assuming it was initially at rest. The mass of the child is 30.0 kg and that of the boat is 35.0 kg. (Take the package's direction of motion as positive.)

Answer 1

0 = mv + (M+m)V; V = - mv/(M + m) = - 5.65kg·10 m/s/(30kg + 35kg) = - 0.87 m/s