Question about Potentials.?

Question

A 5.9g object carries a net charge of 3.9 micro C. It acquires a speed v when accelerated from rest through a potential difference . A 1.8 g object acquires twice the speed under the same circumstances.

What is its charge?

Answer 1

m1=5.9 g, q1=3.9 µC, v1=v

m2=1.8 g,  v2=2*v

Ekin=Work

0.5mv^2=qU

0.5*m1*v1^2=q1*U..................(1)

0.5*m2*v2^2=q2*U..................(2)

Divide (1) by (2) ==>

m1*v1^2/(m2*v2^2)=q1/q2

m1*v^2/[m2*(2v)^2]=q1/q2

m1/(4*m2)=q1/q2

q2=4*q1*m2/m1

q2=4*3.9*1.8/5.9=4.76 µC