$(a)$ Define momentum of a body.
$(b)$ $A$ ball is thrown vertically upward. What is its momentum at the highest point?
$(c)$ State the law of conservation of momentum.

(N/A) Momentum is defined as the product of the mass $(m)$ and velocity $(v)$ of a body. It is given by the formula $p = m \times v$.
$(b)$ At the highest point of its trajectory,the vertical velocity $(v)$ of the ball becomes $0 \ m/s$. Since momentum $p = m \times v$,substituting $v = 0$ gives $p = m \times 0 = 0$. Thus,the momentum at the highest point is zero.
$(c)$ The law of conservation of momentum states that in the absence of an external unbalanced force,the total momentum of a system of objects remains conserved (constant).