Question

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

Answer 1

Hello! I can help you :)
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Newton's third law of motion:

Every action has an equal and opposite reaction.
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When the fireman holds the hose, it has an opposite reaction according to the third law of motion. This backward and an equal reaction on the fireman makes him unstable and finds it difficult to hold the hose. 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

it is difficult for a Fireman to hold a hose which ejects large amount of water at high velocity because of the third law of Newton which states, for every action there is an equal and opposite reaction
As the hose which ejects a large amount of water moving forward has the force which also react the force in the backward direction that's why Fireman hold the host tightly