Answer:
a)

b)

Step-by-step explanation:
Given that
Charge = q
Magnetic filed = B
Radius = R
We know that kinetic energy KE
----------1
m v² = 2 .KE
The magnetic force F = q v B
Radial force

For uniform force these two forces should be equal

q v B R =m v²
q v B R = 2 .KE

Now put the velocity v in the equation

