v = -0.898 m/s.
Work Step by Step
The momentum in the horizontal direction will be conserved. Let the positive direction be the direction in which the package is thrown. The initial momentum is zero. $$0 = (24.0 + 35.0 kg)(v) + (5.30 kg)(10.0 m/s)$$ Solve for v = -0.898 m/s. The negative sign means the boat and child are moving in the opposite direction as the package.