# 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..