Calculating Electric Field Strength to Stop an Electron

[mathcrzy]

Homework Statement

An electron moving to the right at 3% the speed of light enters a uniform electric field parallel to its direction of motion. The electron is to be brought to rest in the space of 6.0cm.
What is the strength of the field?______N/C

Homework Equations

F = q * E

The Attempt at a Solution

Speed = .03 * 3*10^8 = 9,000,000
distance = 6cm = .06m

F = .06 * 9,000,000 = 5.4*10^5 = 5.4*10^2 N/C

 

[rl.bhat]

While calculating the field you have not taken into account the charge and mass of the electron. Here you have to take the relativistic mass.

 

[mathcrzy]

And that would be 50 * 10^-6 ?

 

[rl.bhat]

And that would be 50 * 10^-6 ?
From where did you get this number? What is this?