[填空题]
1.Define momentum.
2.A golf ball of mass $45\,g$ moving with a constant velocity of $2.0\,m\;s^{-1}$ undergoes a head-on collision with a stationary ball of mass $2.0\;kg$. The line that joins the centres of the balls is along the direction of the velocity of the golf ball.
1.Use Newton's Third Law and Second Law to deduce why the change in momentum of the golf ball is equal and opposite to the change in momentum of the stationary ball during the collision.
2.The variation of force acting on the golf ball $F_g$ with the time $t$ during the collision is shown in the graph.
The magnitude of the change in momentum of the golf ball is approximately $kg\,m\,s^{-1}$
3.Calculate the speed of the golf ball just after the collision. $m\,s^{-1}$
4.Discuss whether the collision is elastic or inelastic.
