Suppose two particles 1 and 2 are projected in vertical plane simultaneously.Their angles of projection are 30o and θ, respectively, with the horizontal. Let they collide after a time t in air. Then

If they collide, their vertical component of velocities should be same, i.e., 100sin⁡θ=160sin⁡30∘⇒sin⁡θ=4/5Their vertical components will always be same. Horizontal components:        160cos⁡30=803ms−1and  100cos⁡θ=100×3/5=60ms−1They are not same, hence their velocities will not be same at any time. So (b) is correct.         x=x1−x2=160cos⁡30∘t−100cos⁡θt⇒ x=(803−60)t Time of flight: T=2×160×sin⁡30g=16s (same for both) Now t