Question

A girl is skipping rocks across a lake. One of the rocks accidentally ricochets off a toy boat initially at rest in the water (see the drawing). The 0.063-kg rock strikes the boat at a velocity of 13 m/s, 15^degree below due east, and ricochets off at a velocity of 11 m/s, 12^degree above due east. After being struck by the rock, the boat's velocity is 1.0 m/s, due east. What is the mass of the boat? Assume the water offers no resistance to the boat's motion.

I tried solving it and got 0.11 but it says that its wrong,

Answer 1

In the east direction,
Change in momentum of the stone = momentum gained by the boat.
0.063 [13 cos 15 - 11 cos12] = m *1.0

m = 0.11324 kg.