정답
$\vec{F}_{\text{net}} = m\vec{a} = \frac{d\vec{p}}{dt}$. Impulse $\vec{J} = \vec{F}_{\text{net}}\Delta t = \Delta \vec{p}$, equal to change in momentum.
해설
In an isolated system where external forces sum to zero, total momentum is strictly conserved during all collisions.