Change in momentum = $$\Delta \vec{P}$$

=$$\Delta P_{x}\hat{i} + \Delta P_{x}\hat{j}$$

Since$$\Delta P_{x} = 0$$ $$\Delta P_{y}\hat{j} = \vec{P}_{fy} – \vec{P}_{iy}$$ $$P_{iy} = mvsin45 and P_{fy} = mvsin45$$

=$$– 2mvsin45 = -\sqrt{2}mv_{j}\left | \Delta = \vec{P} \right |$$

=$$\sqrt{2}mv$$

Explore more such questions and answers at BYJU’S.