What is the major important difference between velocity and speed?

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?

What is the relationship between the direction of motion of the balloon and the wind currents

What is the major limitation to the light microscope?