Here we're told that the binding energy of an electrons on a metal surface are 7.15×10-19 J. If an outside energy source with 4.33×10-17 J strikes the metal surface, what would be the kinetic energy of an ejected electron?
So just remember that your total energy, which is Ephoton, equals the binding energy plus your kinetic energy. The total energy of the photon comes from this outside energy source, So that's 4.33×10-17 J equals your binding energy, which is 7.15×10-19 J plus the kinetic energy of the electron ejected.
So subtract out 7.15×10-19 J from both sides O. When we do that, we're going to get left the kinetic energy of the ejected electron. So the kinetic energy here equals 4.26×10-17 J. So this would be the energy, kinetic energy, energy of motion for that ejected electron.