related to projctile motion .

Question

it was calculated that a shell when fired from a gun with a certain velocity and at an angle of elevation 5 pi/ 36 rad should strike a given target in the same horz. plane . 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) 5 pi/36 rad.                                                                                         b) 11 pi/36 rad

c) 7 pi/36 rad                                                                                          c) 13 pi/36 rad

Answer 1

There are two angles of projection for the same horizontal range, i.e; theta and 90 - theta with the horizontal. The projectile will cover the same horizontal range whether it is thrown at an angle of theta or 90 - theta with the horizontal. 

Here when the gun is fired, the shell moves with a certain velocity and the angle of elevation is 5pi/36 = 25 deg 

To overcome the hill which prevents the trajectory, the shell be elevation at an angle of 90 - 25 = 65 deg = 13pi/36, to cover the same range.