A ball moving with a momentum of $5kgm/s$ strikes against a wall at angle of ${45}^{\circ }$ and is deflected at the same angle. Calculate the change in momentum.

Given,

$P=5kgm/s$

$\theta ={45}^0$

from the figure given above, there is no change in perpendicular component and cancel each other.

The initial momentum along the x-axis,

$P_i=Pcos\theta$

The final momentum along the x-axis,

$P_f=-Pcos\theta$

So, change in momentum,

$\Delta P=P_f-P_i$

$\Delta P=-2Pcos\theta$

$\Delta P=-2\times 5\times cos{45}^0$

$\Delta P=-7.071kgm/s$