Speed of Impact of electrons in a television.

[Yavko2510]

Homework Statement

What is the speed of impact of electrons with the screen of the picture tube? Answer in units of m/s.

Electrons are accelerated through a potential difference of 15500 V
Charge of electron: 1.6 x 10^-19 C
Mass of electron: 9.11 x 10^-31 kg
Energy of electrons when they hit the screen: 2.48E-15 J

Homework Equations

v=Ed
f=ma
f=qE
K = .5mv^2

The Attempt at a Solution

I tried using that equation, I made it 15500 = .5mv^2 ... obviously plugging in the above numbers for m and v.

Computer said the answer was wrong.

 

[Delphi51]

Goodness they calculated the electron energy for you! Too easy!

So just use 2.48E-15 J = 1/2mv^2

Potential is the energy per charge, so you could start with V = E/q, and replace E with 1/2mv^2.

 

[Yavko2510]

No, I calculated that for a previous problem...

Thanks though, got it right now.