Find acceleration of an electron

[warnexus]

Homework Statement

An X-ray tube gives electrons constant acceleration over a distance of 20cm . If their final speed is 2.0×107m/s , what are the electrons' acceleration?

Homework Equations

v final ^ 2 = v initial ^ 2 + 2a(x-x initial)

The Attempt at a Solution

x = .2 m (after conversion from cm)
v final is given.

how do I find v initial? I need that so I can find acceleration.

 

[warnexus]

apparently the initial velocity is not zero. I heard 99/100 time it is zero from the internet

 

[frogjg2003]

What did you get as your answer with 0 as the initial velocity?

 

[Redbelly98]

how do I find v initial? I need that so I can find acceleration.

You are correct, without knowing v-initial this problem cannot be solved. The problem author problem meant for v-initial to be zero, but that should have been stated or somehow implied in the problem statement. Did you copy the problem exactly as it was given? Or was there an accompanying figure that somehow gave information about the initial velocity?