Projectile : Two particles are projected horizontally from the same elevated point in opposite directions with velocities 4 m/s and 9 m/s respectively. At the moment when their velocity vectors are mutually perpendicular, the separation between them is (g = 10 m /s2)
a. 7.8m vertically
b. 5.6m vertically
c. 7.8m horizontally
d. 5.6m horizontally