When a hydrogen atom going from n=2 to n=1 emits a photon, its recoil speed is x/5 m / s. Where x= ____. (Use, mass of hydrogen atom =1.6 × 10^-27 kg…

When a hydrogen atom going from $\displaystyle n=2$ to $\displaystyle n=1$ emits a photon, its recoil speed is $\displaystyle \frac{x}{5} \mathrm{~m} / \mathrm{s}$. Where $\displaystyle x=$ $\displaystyle \_\_\_\_$. (Use, mass of hydrogen atom $\displaystyle =1.6 \times 10^{-27} \mathrm{~kg}$ )