A 5-kg fish swimming at 1 m/s swallows an absent-minded 1-kg fish at rest. The speed of the larger fish after lunch is

Question

Quizplus · Accepted Answer

The conservation of momentum principle applies here. Before the larger fish swallows the smaller one, the total momentum of the system is the momentum of the larger fish since the smaller fish is at rest. After swallowing, the total mass is 6 kg. The initial momentum is (5 kg)(1 m/s) = 5 kg·m/s. Since momentum is conserved, the final momentum of the combined mass (6 kg) moving at speed v is also 5 kg·m/s. Solving for v gives v = 5 kg·m/s / 6 kg = 5/6 m/s.

A 5-Kg Fish Swimming at 1 M/s Swallows an Absent-Minded