It was calculated that a shell when fired from a gun with a certain velocity and at an angle of elevation $\frac{5\pi }{36}$ rad should strike a given target. In actual practice, it was found that a hill just prevented the trajectory. At what angle of elevation should the gun be fired to hit the target ?

• A

  $\frac{5\pi }{36} \text{rad}$
• B

  $\frac{11\pi }{36} \text{rad}$
• C

  $\frac{7\pi }{36} \text{rad}$
• Correct answer
  D

  $\frac{13\pi }{36} \text{rad}$

Hence, the correct answer is option: 'D'.