A 540-kg boat, originally at rest, is placed perpendicular to a dock so that the front of the boat touches the dock. A 60-kg boy jumps horizontally at 4.0 m/s from the dock to the front of the boat. The speed of the boat just after the boy jumps in is
A) 0.40 m/s.
B) 0.44 m/s.
C) 1.0 m/s.
D) 4.0 m/s.
E) 4.4 m.

Question

Quizplus · Accepted Answer

Using conservation of momentum, the momentum before the jump (0) equals the momentum after the jump. The equation is: 0 = (60 kg)(4.0 m/s) + (540 kg)(v). Solving for v gives v = -0.44 m/s, but since speed is positive, it is 0.40 m/s.

A 540-Kg Boat, Originally at Rest, Is Placed Perpendicular to a Dock