help me with this one!

hint:

1) The angular momentum is going to be conserved ,because ____

2) Let the speed of the particle when the distance is r₁ be v₁ and when it is r₂ be v₂. The mv₁r₁ = mv₂r₂

3) moreover energy is conserved . i.e Electrostatic Potential energy + kinetic energy of the moving charge is constant.

The idea of the solution is gravitation problems of Irodov.