# Kinetic energy

1. Oct 31, 2006

### stunner5000pt

Determine from classical mechanics (using a head-on collision with recoil at 180 degrees) what fraction of an electron’s kinetic energy can be transferred to a mercury atom in an elastic collision. Derive an approximate value of the fraction.

well ok let the mass of the electron be m_e
initial velocity of electron v_1
fina lvelocity v_2
mercury atom mass m_Hg
mercury atom fina lvelocity v_Hg

$$\frac{1}{2} m_{e} v_{1}^2 = \frac{1}{2} m_{Hg} v_{Hg}^2 + \frac{1}{2} m_{e} v_{2}^2$$

the fraction of kinetic energy is Kf/Ki right

$$\frac{K_{f}}{K_{i}} = \frac{v_{2}^2}{v_{1}^2}$$

do i use momentum concepts to find v2 in terms of v1

still it doesnt give me a numerical value... if thats what the question is asking...

2. Oct 31, 2006

bump :D
for help :)