A photon in motion has a mass

What is the energy of photon whose wavelength is $6840\,\mathop A\limits^o $ ?......$eV$

The frequency of a photon, having energy $100eV$ is$(h = 6.6\,{10^{ - 34}}\,J{\rm{ - }}sec)$

The force on a hemisphere of radius $1\, cm$ if a parallel beam of monochromatic light of wavelength $500\, nm$. falls on it with an intensity of $0.5\, W/cm^2$, striking the curved surface in a direction which is perpendicular to the flat face of the hemisphere is (assume the collisions to be perfectly inelastic)

A beam of electromagnetic radiation of intensity $6.4 \times 10^{-5}\; \mathrm{W} / \mathrm{cm}^{2}$ is comprised of wavelength, $\lambda=310 \;\mathrm{nm} .$ It falls normally on a metal (work function $\varphi=2 \;\mathrm{eV}$ ) of surface area of $1\; \mathrm{cm}^{2} .$ If one in $10^{3}$ photons ejects an electron, total number of electrons ejected in $1 \;s$ is $10^{\mathrm{x}}$.then $\mathrm{x}$ is

$\left(\mathrm{hc}=1240\; \mathrm{eV} \mathrm{nm}, 1\; \mathrm{eV}=1.6 \times 10^{-19} \;\mathrm{J}\right)$

Do all the electrons that absorb a photon come out as photoelectrons ?