A Proton Is Projected Toward a Fixed Nucleus of Charge

Multiple Choice

A proton 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 1/2 v_o.How far from the nucleus will the proton be when its velocity has dropped to 1/4 v_o?

A) 1/16 R
B) 1/4 R
C) 1/2 R
D) 4/5 R
E) None of these