Calculating the Distance Fallen by an Electron Beam

[Warmacblu]

Homework Statement

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.

Homework Equations

x = v_oxt

v_y = v_oy - gt

The Attempt at a Solution

I solved for t:

x = v_oxt

.04 = 2.5 x 10⁷
t = 1.6 x 10^-9

Then I plugged t into v_y = v_oy - gt.

v_y = 0 - (9.8)(1.6x10^-9)
v_y = -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.

 

[rl.bhat]

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

 

[Warmacblu]

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

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

 

[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.