Question

A fisherman in a boat catches a huge fish with a rod and starts to pull it in. The fish
struggles for a while and then becomes still when it is at a distance of 200 m from the
boat. During this operation, the boat (initially at rest) moves 25 m in the direction of the
fish. If the mass of the boat is 5000 kg, calculate the mass of the fish. Assume that water
exerts no friction

Answer 1

Answer on question #61698, Physics / Mechanics

Question A fisherman in a boat catches a huge fish with a rod and starts to pull it in. The fish struggles for a while and then becomes still when it is at a distance of 200 m from the boat. During this operation, the boat (initially at rest) moves 25 m in the direction of the fish. If the mass of the boat is 5000 kg, calculate the mass of the fish. Assume that water exerts no friction

Solution The center of mass doesn't move, as sum of momentums is constant. Hence, moving of boat is compensated by moving of fish

$$m _ {1} x _ {1} = m _ {2} x _ {2}$$

Mass of fish is

$$m _ {2} = \frac {x _ {1}}{x _ {2}} m _ {2} = \frac {2 5}{2 0 0} \cdot 5 0 0 0 = 6 2 5 k g$$

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