# Homework Help: Motion in 2d w/ constant acceleration

1. Sep 16, 2007

### luna02525

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

In a tv set, an electron beam moves with horizontal velocity 2.7 x 10^7 m/s across the cathode ray tube and strikes the screen, 42 cm away. The acceleration of gravity is 9.8 m/s^2.

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

2. Relevant equations

x-direction:

$$v_{xo} = 2.7 x 10^7 m/s$$
$$\Delta{x} = .42 m$$

y-direction:
$$a_{y} = 9.8 m/s^2$$
$$\Delta{y} = ? m$$

$$a_{y} = 9.8$$
$$v= 9.8t + v_{y0}$$
$$y= 4.9t^2 + v_{y0}t + y_{0}$$

3. The attempt at a solution

I first tried to solve for time:

$$.42 = 2.7*10^7(t)$$
$$t = 1.556*10^{-8}$$

Then, I tried solving for $$\Delta{y}$$

$$\Delta{y} = v_{0y}t + (1/2)gt^2$$
$$\Delta{y} = 0 + 4.9(1.556*10^{-8}$$
$$\Delta{y} = 1.186*10^{-15}$$

however, this is turning up as incorrect. Where did I go wrong? What am I doing incorrectly?

Last edited: Sep 16, 2007
2. Sep 16, 2007

### Staff: Mentor

Looks OK to me. What makes you think it's wrong?

(If it's an on-line system, be sure to use a reasonable number of significant figures.)

3. Sep 16, 2007

### luna02525

It was indeed my significant figures!

Thanks for taking a look at my work. I was afraid I was completely off.