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

The stream of water ejecting from the nozzle of the hose goes in the forward direction with a force.

As a reaction (Newton's third law of motion), the hose is pushed back with equal force.

That is why is difficult for a fireman to hold the hose.

Answer 2

The ejection of a large amount of water at a high velocity from a hosepipe results in the development of an equal force of reaction 

on the hosepipe in the backward direction. That is why it becomes difficult for the fireman to hold the hosepipe.