Initial velocity is calculated as, vi=u‌cos‌θ‌
^
i
+u‌sin‌θ‌
^
j
vi=10√3‌cos‌60°‌
^
i
+10√3‌sin‌60°‌
^
j
vi=5√3
^
i
+15
^
j
Final velocity is calculated as, vf=u‌cos‌θ‌
^
i
+(u‌sin‌θ−gt)
^
j
vf=5√3
^
i
−5
^
j
The dot product of both velocities is, vi.vf=25×3−15×5 vi.vf=0 The dot product is zero, so both the velocities are perpendicular to each other. vi⊥vf