Physics 30 Matteri would apresiate some help on this question

1. Dec 29, 2007

cathoderay

[SOLVED] physics 30 ...Matter..i would apresiate some help on this question ..

hi this is a cuestion from physics 30 grde 12 ...i need some help figuring out how to solve it ...the provlem is as folow..
1. x-rays of wavelenght 5.0 x 10^-11m strike a free electron at rest. The free electron rebounds with a velocity of 2.0 x 10^6 m/s. The Scattered X-ray strikes a metallic surface whose work function is 5.2 x 10^-16J.

What is the maximum velocity of an emitted photoelectron?
a)2.0 x 10^6 m/s
b)8.7 x 10^7 m/s
c)4.3 x 10^4 m/s
d)5.4 x 10^5 m/s

3. this is what i have done but im just confuse now ..im not sure if this is right:

Ek=hf-hf'
f'=w/h
=5.2 X 10^-16/6.63 x 10^-34
=7.85 x 10^17HZ

E=hc/λ
=(6.63 x 10^-34)(3.00 x 10^8)/5.0 x 10^-11m
=3.978 x 10^-15J

f=E/h
=3.978 x 10^-15/6.63 x 10^-34
=6 x 10^18HZ

Ek=hf-hf'
=(6.63 x 10^-34)(6 x 10^18) - (6.63 x 10^-34)( 7.85 x 10^17)
=3.46 x 10^-15J

v=Ek/q
=3.46 x 10^-15J/1.60 x 10^-19c
=2.2 X 10^4

there im stuck im not sure what else to do ..what formula was i supose to use..am i in the right way or not..? if there is someone that could help me solve this problem... it will be grate ..thanks..

2. Dec 29, 2007

mjsd

what is this last step?

use $$E_k = \frac{1}{2} m v^2$$ for electron is ok here as gamma (from relativity) is only about 1.

3. Dec 29, 2007

Thanks..