Question

Two second after projection a projectile is travelling in a direction inclined at $30^{\circ}$ with horizontal, after one more second it is travelling horizontally. Angle of projection (in degree) with horizontal divided by $10$ is.

Answer 1

Let angle made by $\vec{v}$ initially and after time $t$ be $\theta$ and $\alpha$ respectively.
$\tan 30^{\circ}=\frac{u \sin \theta-g \times 2}{y \cos \theta} \ldots \ldots \ldots $ (i)
$\tan 0^{\circ}=\frac{u \sin \theta-g \times 3}{u \cos \theta} \ldots \ldots \ldots . .$ (ii)
$\therefore \theta=60^{\circ}$