A projectile is thrown from the base of an incline of angle ${30}^{\circ }$. It is thrown at an angle of ${60}^{\circ }$ from the horizontal direction at the speed of $20\text{m/s}$. Find the total time of flight.$(g=10{\text{m/s}}^2)$

The correct option is D $\frac{4}{\sqrt{3}}\text{s}$
Given:
Angle of incline$\left(\alpha \right)={30}^{\circ }$
Angle of projection with horizontal$(\theta +\alpha )={60}^{\circ }$
Speed of projection$=20\text{m/s}$

Since the formula for time of flight is
$T=\frac{2u\sin \theta }{g\cos \alpha }=\frac{2\times 20\times \sin {30}^{\circ }}{10\times \cos {30}^{\circ }}=\frac{4}{\sqrt{3}}\text{s}$

Hence, option $\left(\text{C}\right)$ is the right choice.