Question

the amount of work done to move a positive point charge q on an equipotential surface of 8000 V relative to that on an equipotential surface of 70 V is ?

Answer 1

When you move a charge in equipotential surface or line, you don't require any energy. The energy required is U = q*(V1-V2). In equipotential surface, V1=V2. So, the answer to the question: no need energy to move a charge in equipotential surface of 8000 V, and no need energy to move charge in equipotential surface of 70 V either.