Posted by Shaniquaa on .
When light of a wavelength of 125 nm strikes a certain metal, electrons having a velocity of 8.2 x 10^5 m/s are
emitted from the surface of the metal. What is the threshold frequency of the metal?
The answer is 1.9 x 10^15 s^1
I'm not sure how to do this. The equations that I tried to use were E=1/2mv^2, E=hfhf0, E=hc/lamda but it didn't work

Chemistry 
DrBob222,
KE = (hc/w)hf
KE = 1/2(m)(v^2) so
1/2(m)(V)^2 = (hc/wavelength)  hf.
You have m in kg, v in m/s, h, c, and wavelength (w in meters). Solve for f.
I get 1.9 x 10^15 Hz.