Question

If a stone is projected from ground with a velocity 50 $m{s}^{-1}$ and at an angle of ${30}^o$, it takes 3 s to cross a wall. How far beyond the wall the stone will strike the ground?
(Take g = 10 $m{s}^{-2}$)

• A. 50.5 m
• B. 91.5 m
• C. 86.6 m
• D. 100 m

Answer 1

The correct option is C 86.6 m

Total time of flight
$=\frac{2u\sin \theta }{g}=\frac{2\times 50\times 1}{2\times 10}=5s$
Time to cross the wall = 3 s
$\therefore$ Time in air after crossing the wall
$=(5-3)=2s$
So, distance travelled beyond the wall
$=\left(u\cos \theta \right)t=50\times \frac{\sqrt{3}}{2}\times 2=86.6m$