Motion

A projectile is projected with velocity of $ 40 \mathrm{~m} / \mathrm{s} $ at an angle $ \theta $ with the horizontal. If $ R $ be the horizontal range covered by the projectile and after $ t $ seconds, its inclination with horizontal becomes zero, then the value of $ \cot \theta $ is [Take, $ g=10 \mathrm{~m} / \mathrm{s}^{2} $ ]