Question

A stone is projected from the ground with velocity $50\text{m/s}$ at an angle of ${30}^{\circ }$. It crosses a wall after $3\text{sec}$. How far (approx) beyond the wall the stone will strike the ground ? $(g=10{\text{m/sec}}^2)$

• A. 86.6
• B. 85
• C. 87
• D. 86

Answer 1

Answer: (A), (B), (C), (D)

Given:
$u=50\text{m/s},\theta ={30}^{\circ }$
Total time of flight
$=\frac{2u\sin \theta }{g}=\frac{2u\sin {30}^{\circ }}{g}=\frac{2\times 50\times 1}{2\times 10}=5\text{sec}$
Time to cross the wall $=3\text{sec}$ (given)
Time for which stone remain in air after crossing the wall
$=(5–3)=2\text{sec}$
$\therefore$ Distance travelled beyond the wall $=\left(u\cos \theta \right)t=\left(u\cos {30}^{\circ }\right)t$
$=50\times \frac{\sqrt{3}}{2}\times 2=86.6\text{m}$