what happens to the photon which strikes an electron in themetal sheet?

Photon is a tiny packet of light energy which gets absorbed to liberate photoelectrons.

One photoelectron is ejected from a metal surface if one photon of suitable radiation falls on it. A part of its energy is used in liberating the electron from the metal surface which is equal to the work function of the metal. The rest of the energy is used on imparting kinetic energy to the emitted photon.

 

So, the photon, which is nothing but a packet of energy, gets completely absorbed during the process.