A proton of mass m is moving with initial speed v 0 toward an particle of

A proton of mass m is moving with initial speed v₀ toward an α particle of mass 4m, which is initially at rest. Because both particles carry positive electrical charge, they repel each other.

Find the speed v' of the α particle

(a) When the distance between the two particles is least,

(b) When the two particles are far apart.