The momentum of a photon of energy $1 \text{ MeV}$ in $\text{kg-m/s}$ will be

Light of wavelength $5000 \, \mathring{A}$ falls on a sensitive surface. If the surface has received $10^{-7} \, \text{J}$ of energy,then the number of photons falling on the surface will be:

When an $X$-ray photon collides with a proton,its frequency:

Consider a hypothetical annihilation of a stationary electron with a stationary positron. What is the wavelength of the resulting radiation? ($h =$ Planck's constant,$c =$ speed of light,$m_0 =$ rest mass)

Number of photons of equal energy emitted per second by a $6 \ mW$ laser source operating at $663 \ nm$ is . . . . . . . (Given: $h=6.63\times10^{-34} \ J.s$ and $c=3\times10^{8} \ m/s$)

The rest mass energy of an electron is $0.51 \ MeV$. If this electron is moving with a velocity of $0.8 \ c$ (where $c$ is the velocity of light in vacuum),then the kinetic energy of the electron is ........... $MeV$.