# Homework Help: Electric force-finding coordinate

Tags:
1. Sep 2, 2015

### psysicsfeet

1. The problem statement, all variables and given/known data
The y-axis marks the boundary between the area where the is no electric field (in the second and third quadrant) and the area where there is a constant electric field: E = 610j N/C (in the first and fourth quadrant).

An electron travels along the negative x-axis toward the origin at vo = 7.04i Mm/s, and then it enters the electric field.and changes direction. Find the y-coordinate of the electron, in cm, when its x-coordinate is 92.3 cm.

2. Relevant equations
following two formulas may be useful I do not know

E=kq/r^2
F=qE
I suppose to use a formula that relate with value v0 I guess.
3. The attempt at a solution
Anyone can help me figure it out. thank you. I do not have any idea of it.

2. Sep 3, 2015

### ehild

First make a drawing: A coordinate system, and indicate the region with E=0 and E = 610j. Show the electron travelling along the negative x axis towards the origin with velocity v0 = 7.04i Mm/s.
What force acts on the electron when it is in the electric field?

3. Sep 3, 2015

### rude man

This is exactly analogous to a projectile fired with a horizontal initial velocity v0, with the E field, like gravity, acting in the -j direction (no air resistance assumed, as usual). The E field is equivalent to gravity.

BTW in this problem, mass of the electron is ignored. The force is electrostatic only.

4. Sep 3, 2015

### ehild

I think you meant that gravity is ignored.