Homework Help: Electrons subjected to a continuous force

1. Nov 10, 2008

abotiz

Hi there!

I got some difficulty understanding a question regarding electrons

Electrons which are initially at rest are subjected to a continuous force of 2E-12 N
along a lenght of 2 miles and reach very near the speed of light.

a) Determine how much time is required to increase the electrons speed from 0.93c to 99c

b) Approximately how far does the electron go in this time? What is approximate about your result?

The Impuls = mv1-mv0 Where m is the electrons mass ( 9.109 E-31) and v1=0.99C and v0=0.93C

So I get the Impuls, and then I= F*t I divide the Impuls with the force ( 2E-12) and get the time 8.19E-12 is this right?

And b) I use vt=s where v is 0.99C and get the lenght 2.43E-3

Have a made a mistake somewhere? Also, I dont understand the second question in b) " What is approximate about your result? "

Thank you

2. Nov 11, 2008

Hootenanny

Staff Emeritus
You're answer varies from the books because your applying classical mechanics to a relativistic particle.

Try using relativistic mechanics.

3. Nov 11, 2008

abotiz

Okay, so I should be using this instead?

If I do, I get the time 2.767E-11 s

And the meters it travells would be 0.016 m ( here I used (0.93c+0.99c) multiplied with the time, is this right or should I just have 0.99c)

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