Explain,why is it difficult for a fireman to hold a hose,which ejects large amounts of water at a high velocity.

(N/A) The difficulty arises due to the backward reaction force of the water being ejected.
When a fireman holds a hose that ejects a large volume of water at a high velocity,the water exerts an equal and opposite reaction force on the hose in the backward direction,according to $Newton's$ third law of motion.
This backward force pushes the fireman,making it difficult for him to maintain his balance and stability while holding the hose.