1. Apr 27, 2005

### glitterjewels

Here's the problem:
Electrons with initial speed of 5 x 10^6 m/s are projected into a region where a constant electric field of 1 x 10^5 V/m exists. The field is directed in a way that causes the electrons to DECELERATE. How far do the electrons travel before they turn around and move in the opposite direction?

My problem is I'm not sure how to find the distance or "how far". I may be missing an equation. Here's what I do have

F/m=acceleration=Fg=mg
The electric field=qE(volts/m)= 1 x 10^5 V/m
charge of electron qe= 1.06 x 10^-19c
acceleration upward= qE/m
Your help would be greatly appreciated! Thank you!

2. Apr 27, 2005

### xanthym

Since motion direction isn't specified, it's presumed gravitational effects can be ignored. For these conditions, the following kinematic equation applies:

$$1: \ \ \ \ v_{final}^{2} \, - \, v_{initial}^{2} \, \ = \, \ 2 a d$$

where "v"s are the indicated velocities (here: vfinal=0, & vinitial=5e6 m/s), "d" the distance traveled, and "a" the constant acceleration (here: a=qE/m). Solve for "d".

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Last edited: Apr 27, 2005