What is the momentum of an object at rest, in m/s?

Aproton is projected toward a fixed nucleus of charge +ze with velocity vo. initially the two particles are very far apart. when the proton is a distance r from the nucleus its velocity has decreased to 1/2vo. how far from the nucleus will the proton be when its velocity has dropped to 1/4vo?

Which object is most likely represented by a dot?

What are atoms of the same element with varying number of neutrons