Give reasons and state the laws related to these statements:
$(a)$ It is easier to push an empty box than to push a box full of books.
$(b)$ It is difficult for a fireman to hold a hose which ejects a large amount of water with high velocity.

(N/A) This is based on Newton's $\text{Second}$ Law of Motion $(F = ma)$. An empty box has less mass, and therefore less inertia, compared to a box full of books. Since force is directly proportional to mass, less force is required to accelerate the empty box.
$(b)$ This is based on Newton's $\text{Third}$ Law of Motion (Action and Reaction). When water is ejected from the hose with high velocity in the forward direction, it exerts an equal and opposite reaction force on the hose in the backward direction. This makes it difficult for the fireman to hold the hose steady.