Point Charges on a Triangle

Question

Three identical point charges are released from rest at the corners of an equilateral triangle with sides 0.8m. Each charge has a charge of +1.2 μC and a mass of 5.4 x 10^-3 kg. Find the speed of the charges when their distance from the center of the triangle doubles.

 

 

I'm getting the wrong answer

...............

 

E_pi= 3E_k + E_pf

0.0486 = 3•0.5•mv² + 0.0162

 

v=2 m/s but the answer should be 3 m/s

 

Answer 1

The PE IN THE FINAL STAGE IS NOT 1/4 TH OF INITIAL 

But only half 

so replace 0.0162 by 0.0243 to get the answer 

For PE 

PE =3* Kq1*q2/ r and 3*Kq1* q2/R

as r= 0.8 m and R = 1.6m
and R = 2r