Photoelectric Effect Question

[Amber Shanks 2K]

The question asks " A metal absorb radiation with a minimum frequency of 2.1X10^15 Hz before it can emit an electron from its surface via the photoelectric effect. What is the minimum energy required to produce this effect?" My question is why does the KE become 0?

[505934309]

The kinetic energy is the energy that the electron has after being ejected. It only has this energy when there is an excess of energy when it is ejected that it then absorbs. Therefore if it is ejected with the minimum amount of energy required, it will have no KE because it's not absorbign any extra. Hope this helps!