Question

A ball is thrown from ground level so that it just clears a wall $3m$ high when it is moving horizontally, if the initial speed of the ball is $20m/s$, find the angle of projection.[$g=10m/s^2$]

Answer 1

Since,it clears wall high when it is moving horizontally 3 meter is its maximum height.

$\Rightarrow \frac{u^2{\sin }^2\theta }{2g}=3m$

Also, $u=20m/s$

$\Rightarrow \frac{{20}^2{\sin }^2\theta }{20}=3$

$\Rightarrow {\sin }^2\theta =\frac{3}{20}$

$\Rightarrow \theta ={\sin }^{-1}\sqrt{\frac{3}{20}}$

$={22.78}^0$