# Uniform electric field and a proton

1. Sep 20, 2009

### tag16

1. The problem statement, all variables and given/known data
A proton moves at 4.50x10^5 m/s in the horizontal direction. It enters a uniform vertical electric field with a magnitude of 9.60x10^3 N/C. Ignoring any gravitational effects, find a) the time interval required for the proton to travel 5.00 cm horizontally b) its vertical displacement during the time interval in which it travels 5.00 cm horizontally c) the horizontal and vertical components of its velocity after it has traveled 5.00 cm horizontally.

2. Relevant equations
a= qE/m

3. The attempt at a solution

I know I need to use the above equation at some point in this problem but I have no idea how to go about finding the time interval.

2. Sep 20, 2009

### tiny-tim

Hi tag16!

Treat this exactly as you would a projectile under gravity …

calculate the acceleration, and do the x and y components separately.

3. Sep 20, 2009

### tag16

ok for the formula for acceleration a=qE/m how do you find E? q= 9.60x10^3 right? thanks

4. Sep 21, 2009

### tiny-tim

(try using the X2 tag just above the Reply box )
No, q is charge, and is in coulombs (C)

E is the field, in newtons per coulomb (N/C) … E = 9.60x103

5. Sep 21, 2009

### tag16

ok...not sure how to figure out q then since it's not given in the problem.

6. Sep 21, 2009

### tiny-tim

It's the same as the charge on an electron (times minus-one, of course) … does that help?

7. Sep 21, 2009

### tag16

oh yeah I forgot about that...1.602x10^-19