How fast is the smaler sphere moving when they collide?

[sonnycorleone]

Homework Statement

Two insulating spheres having radii 0.15cm and 0.69 cm, masses 0.15 kg and 0.69 kg, and charges −3 μC and 2 μC are released from rest when their centers are separated by 1.5 m. How fast is the smaller sphere moving when they collide? Answer in units of m/s.


I am completely lost. Somebody please help solve this...

 

[ehild]

What force acts between the spheres? Are there any external forces? How close can they get to each other? What is their kinetic energy? What is the mutual potential energy of the two balls?

ehild