Question

A 20-kg fish swimming at 1 m/s swallows a 5-kg fish swimming toward it at a velocity that bring both to a halt. How fast was the smaller fish moving prior to being eaten?

Answer 1

Swallowed fish speed=4 m/s

Step-by-step explanation:

Given

m₁(fish mass)=20 kg

v₁(fish speed)=1 m/s

m₂(Swallowed fish mass)=5 kg

To find

v₂(Swallowed fish speed)

Solution

From law of conservation of momentum

`m_(1)v_(1)+m_(2)v_(2)=(m_(1)+m_(2))v\\ (20kg)(1 m/s)+(5 kg)v_(2)=(20kg+5kg)0m/s\\20kg.m/s+5kgv_(2)=0\\v_(2)=(20kg.m/s)/5kg\\v_(2)=4m/s`

As I neglected the negative sign because it only shows that swallowed fish is moving in opposite direction