Atoms And Nuclei

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