Question

Like charges repel. what about protons in a nucleus which have positive charge but they don't repel

Answer 1

The protons in the nulues does repel each other,that is why they dont clolide with each other,but the nuclear force is stronger than the repulsive force ,hence the protons are held together.

The strong nuclear force is responsible for holding together the nucleus. At the distance scale of a proton (about 1 femtometer, or 10−1510−15 meters), the strong nuclear force is about 137 times stronger than the electromagnetic force(repulsive force). Therefore, the repulsive force due to both the protons being electrically positive is not strong enough to break the nucleus apart.
I hope this helps :)