If de Broglie wavelength of an electron is $10 \stackrel{°}{\mathrm{A}}$, then its velocity will be:

The energy of an $\alpha$-particle having de Broglie wavelength of $0.004\stackrel{\circ }{ \mathrm{A}}$ is:

The velocity of a proton is $\frac{c}{20}$. The de Broglie wavelength associated to it is: (Here $c$ is the speed of light.)

A hydrogen atom moving at a speed $v$ absorbs a photon of wavelength $122 \mathrm{nm}$ and stops. Find the value of $v$.

(Mass of hydrogen atom$=1.67\times {10}^{-27 }\mathrm{kg}$)