Answer:

Step-by-step explanation:
It is given that,
Charge on helium nucleus is 2e and its mass is

Speed of nucleus at A is

Potential at point A,

Potential at point B,

We need to find the speed at point B on the circle. It is based on the concept of conservation of energy such that :
increase in kinetic energy = increase in potential×charge

So, the speed at point B is
.