Explain, why is it difficult for a fireman to hold a hose pipe

Solution:
We can explain the above observation on the basis of law of conservation of momentum. When the system of hose and water is not ejecting any water, its momentum is zero. When the water issues out from the hose with a high velocity, it has momentum in the forward direction. Therefore, in order to conserve momentum, the hose tends to move in the backward direction and hence is difficult to hold.
or
The ejection of large amounts 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.