Answer
speed of ping pong ball $v=4.18559\times10^{-22}m/s$
Work Step by Step
Wavelength of the photon of red light is
$\lambda=720nm=720\times10^{-9}m=7.2\times10^{-7}m$
Momentum of the photon is given by $p=\frac{h}{\lambda}$
putting $h=6.63\times10^{-34}J.s$ and $\lambda=7.2\times10^{-7}m$
so $p=\frac{6.63\times10^{-34}J.s}{7.2\times10^{-7}m}=0.920833\times10^{-24}kg.m/s$
$p=9.2083\times10^{-25}kg.m/s$
given that photon of red light and ping pong ball have the same momentum
so momentum of pin pong ball $p_{ppb}=9.2083\times10^{-25}kg.m/s$
given mass of ping pong ball $ m=2.2\times10^{-3}kg$
assuming speed of ping pong ball to be $v$ ,its momentum will be
$p_{ppb}=m\times v$
so speed of ping pong ball $v=\frac{p_{ppb}}{m}$
so speed of ping pong ball $v=\frac{9.2083\times10^{-25}kg.m/s}{2.2\times10^{-3}kg}$
so speed of ping pong ball $v=4.18559\times10^{-22}m/s$
