# Electron Beam

1. Sep 6, 2009

### Warmacblu

1. The problem statement, all variables and given/known data

In a TV set, an electron beam moves with horizontal velocity of 2.5 x 107 across the cathode ray tube and strikes the screen, 40 cm away.

The acceleration of gravity is 9.8 m/s2.

How far does the electron beam fall while traversing this distance? Answer in units of m.

2. Relevant equations

x = voxt

vy = voy - gt

3. The attempt at a solution

I solved for t:

x = voxt

.04 = 2.5 x 107
t = 1.6 x 10-9

Then I plugged t into vy = voy - gt.

vy = 0 - (9.8)(1.6x10-9)
vy = -1.568x10-8

Now I am not sure if I have the correct values plugged in because I do not think I am supposed to come up with a negative answer. I did draw a picture but am not sure if my math corresponds to the picture.

Any suggestions are appreciated,
Thanks.

2. Sep 6, 2009

### rl.bhat

vy = voy - gt
Check this formula.
If vy and g are in the same direction, they must have the same sigh.

3. Sep 6, 2009

### Warmacblu

Thanks for the quick reply. I will think about it while I sleep and report back tomorrow morning.

4. Sep 7, 2009

### Warmacblu

I figured out my mistake. I divided the 40 cm distance by 1000 instead of 100 which gave me the incorrect time. I solved for time again and plugged that into y = 1/2gt^2 which gave me the correct answer.