A point mass having mass $M$ is moving with a velocity $V$ at an angle $\theta$ to the wall as shown in the figure. The mass undergoes a perfectly elastic collision with the smooth wall and rebounds. The total change (final minus initial) in the momentum of the mass is
- $-2MV \cos\theta \hat{j}$
- $2MV \sin\theta \hat{j}$
- $2MV \cos\theta \hat{j}$
- $-2MV \sin\theta \hat{j}$