A 20 kg fish swimming at 2 m/s swallows a 5 kg fish at rest. What is the speed of the large fish after lunch

1.6m/s

Explanation:

Given parameters:

Mass of the big fish  = 20kg

Mass of small fish = 5kg

Speed of big fish  = 2m/s

Speed of small fish = 0m/s

Unknown:

Speed of the large fish after lunch  = ?

Solution:

The momentum of the big fish before and after feeding is conserved.

    Initial momentum  = Final momentum

    m₁v₁ + m₂v₂  = v (m₁ + m₂)

m₁ is mass of the big fish

v₁ is the speed of the big fish

m₂ is mass of the small fish

v₂ is the speed of the big fish

v is the final speed

 Now insert the parameters and solve;

       20 x 2 + 5(0) = v(20 + 5)

              40 = 25v

                v  =   = 1.6m/s

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