college physics
posted by Ace on .
The electrons that produce the picture in a TV set are accelerated by a very large electric force as they pass through a small region in the neck of the picture tube. This region is
1.4 cm in length, and the electrons enter with a speed of 1× 105 m/s and leave with a speed of 1.5 × 108 m/s.
a. What is their acceleration over this 1.4 cm length? Answer in units of m/s2.
b. How long is the electron in the accelerating region? Answer in units of s.

BE CAREFUL OF UNITS
The neck length is in cm!
For a constant acceleration:
s = distance
v1 = initial velocity
v2 = final velocity
a = acceleration
t = time
s = (v1)(t) + (1/2)(a)(t^2)
s and v1 are given
v2 = v1 + (a)(t)
so (a)(t) = v2  v1
v1 and v2 are given
substitute for (a)(t) in the first equation to solve for time.
acceleration = dv/dt = (v2  v1)/t 
i did not understand that! I NEED HELP!