chemistry
posted by Emily .
Light with a wavelength of 405 nm fell on a strontium surface, and electrons were ejected. If the speed of an ejected electron is 3.49 105 m/s, what energy was expended in removing the electron from the metal? Express the answer in joules (per electron) and in kilojoules per mole (of electrons).

KE = hc/wavelength  work function so
1/2*m*v^2 = hc/wavelength  work function. solve for work function. The answer is about 4 x 10^19 J/electron and that x 6.022E23 for a mole of electrons. This is an approximate answer; you need to go through it with a little more accuracy. I used 9.11 x 10^31 Kg for m, 6.626E34 J.s for h and 3E8 m/s for c.