Help with physics problem!?

Question

Across what potential difference does an electron have to be accelerated in order to reach the speed v = 2 x 10 to the 7 m/s? should you use relativistic calculations?

Answer 1

Ke=Pe
Ke=0.5 mv^2
Pe= Vq

V= 0.5 m v^2/q

q= -1.602E-19 C
m= 9.109 E-31 kg

Use relativistic calculations...? Well you may, but

(v/c)^2= (2E+7/ 3E+8)^2=0.0044 would influence the rest mass by

1/(1-0.0044)= 1.0045 or 0.45%