A truck is moving with a constant velocity of `54 km h^-1`. In which direction (angle with the direction of motion of truck) should a stone be projected up with a velocity of `20 ms^-1`, from the floor of the truck of the truck, so as to appear at right angles to the truck, for a person standing on earth ?

Explanation

Let the stone be projected at an angle `prop` to the direction of motion of truck, with a speed of `20 m s^-1`.
Since the resultant displacement along horizontal is zero, the velocity along horizontal = 0
`15 + 20 cos prop = 0`
`cos prop = -(3)/(4) rArr prop = cos^-1 ((-3)/(4))`.