Answer:
0.85 c
Explanation:
When the two travel at right angles to each other , their relative velocity is given by the hypotenuse formed by the x and y direction velocities.
Relative velocity of the two protons is given as
[tex]\sqrt{v^{2}+v^{2}} = (\sqrt{2} ) v[/tex]
If v = 3/5 c , then the relative speed = [tex]\sqrt{2}[/tex] (3/5c) =0.85 c