Question

A ball is projected from ground with speed 10 m/s, then the minimum angle of projection so that the ball lands on the 2nd stair is

• A. ${10}^{\circ }$
• B. ${30}^{\circ }$
• C. ${15}^{\circ }$
• D. ${7.5}^{\circ }$

Answer 1

The correct option is C ${15}^{\circ }$

$R=\frac{u^{2}sin2\theta }{g}$

If ball just crosses 1st stair, it will land on 2nd stair $\Rightarrow R\simeq 4.5+0.5=5=\frac{u^{2}sin2\theta }{g}=\frac{10\times \text{/}10\times sin2\theta }{\text{/}10}$

$sin2\theta =0.5\Rightarrow \theta ={15}^{\circ }$