A ball of mass m collides with a vertical wall with an initial horizontal speed u and rebounds with a horizontal speed v. The graph shows the variation of the speed of the ball with time.

What is the magnitude of the mean net force on the ball during the collision?

A.     $\frac{{m(u - v)}}{{({t_2} + {t_1})}}$

B.     $\frac{{m(u - v)}}{{({t_2} - {t_1})}}$

C.     $\frac{{m(u + v)}}{{({t_2} + {t_1})}}$

D.     $\frac{{m(u + v)}}{{({t_2} - {t_1})}}$

D