Question

What speed does a $H_2$ molecule have if it has the same momentum as a photon of wavelength 280 nm?
(take mass of 1 $H_2$ molecule $=3.32\times {10}^{-27}kgandh=6.63\times {10}^{-34}Js$)

Answer 1

momentum of photon=$\frac{h}{\lambda }=\frac{6.63\times {10}^{-34}Js}{280\times {10}^{-9}m}=2.36\times {10}^{-27}$
$P=m\times v=2.36\times {10}^{-27}$
Speed of $H_2$ =$\frac{2.36\times {10}^{-27}}{3.32\times {10}^{-27}}=0.71m{s}^{-1}$