Question

explain why is it difficult for the Fireman to hold a hose which ejects large amount of water at a high velocity

Answer 1

Every action has an equal and opposite reaction. When the fireman holds the hose, it has an opposite reaction according to the third law of motion. ... Thus, due to the opposite reaction of the water with high velocity a fireman finds it difficult to hold the hose.

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Answer 2

The Newton's third law of motion states that for every action there is an equal and opposite reaction.
So when large amount of water ejects with a large force it applies a large force on pipe in backword direction so it is difficult for fireman to hold the hose