A stone is projected from ground with velocity 50 ,m/s at an angle of {30^o} . It crosses a wall aft

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3-2.Motion in Plane

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

A

$90.2$

B

$89.6$

C

$86.6$

D

$70.2$

Solution

(c) Total time of flight $ = \frac{{2u\sin \theta }}{g} = \frac{{2 \times 50 \times 1}}{{2 \times 10}} = 5\,s$

Time to cross the wall $= 3$ sec (given)

Time in air after crossing the wall $= (5 -3) = 2 \,sec$

$\therefore$ Distance travelled beyond the wall $ = (u\cos \theta )t$

$ = 50 \times \frac{{\sqrt 3 }}{2} \times 2 = 86.6\,m$

Standard 11

Physics

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