Question

A ball of mass $5Kg$ strikes against wall at an angle of ${45}^o$ and is reflected at the same angle. Find the change in momentum.

Answer 1

Given,

Mass $M=5kg$

Incident angle is ${45}^o$

Reflected angle is $({90}^0+{45}^o)$

$V_{initial}=V\cos {45}^o\hat{i}+V\sin {45}^o\hat{j}=\frac{V}{\sqrt{2}}\hat{i}+\frac{V}{\sqrt{2}}\hat{j}$

Final velocity

$V_{final}=V\cos ({90}^o+{45}^o)\hat{i}+V\sin ({90}^o+{45}^o)\hat{j}$

$V_{final}=-\frac{V}{\sqrt{2}}\hat{i}+\frac{V}{\sqrt{2}}\hat{j}$

Change in momentum $\Delta P=mass\times (V_{final}-V_{initial})=5\times \frac{V}{\sqrt{2}}\hat{j}$

Magnitude of Change in momentum $\left|\Delta P\right|=\frac{5V}{\sqrt{2}}kgm/s$