A projectile is projected with velocity of 40 ~m / s at an angle 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 is [Take, g=10 ~m / s ^2 ]
A. R 20 t^2
At maximum height, inclination with horizontal becomes zero. Time (taken by) projectile to reach maximum height, aligned t & = u g \\ u & = g t (i) aligned Since, R=u (2 t) aligned & = R 2 u t \\ & = R 2 g t t \\ & = R 2 g t^2 (Using(i)) aligned = R 2 g t^2 = R 2 10 t^2 = R 20 t^2
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