From Newton’s third law, we know that every action has an equal and opposite reaction. So when a fireman holds a hose-pipe which is ejecting a large amount of water at high velocity experiences a backward push due to the force of water flowing in the forward direction. Hence making it clear that due to the action of force in the forward direction the force is applied on the pipe in the backward direction, thus making the fireman difficult to hold the hose-pipe.
