Two seconds after projection a projectile is travelling in a direction inclined at 30^o to&nbsp

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3-2.Motion in Plane

hard

Two seconds after projection a projectile is travelling in a direction inclined at $30^o$ to horizontal, after one more second it is travelling horizontally. What is the magnitude and direction of its velocity at initial point

A

$20 \sqrt 3 \,m/s, 30^o$

B

$20 \sqrt 3 \,m/s, 60^o$

C

$10 \sqrt 3 \,m/s, 30^o$

D

$10 \sqrt 3 \,m/s, 60^o$

Solution

$\mathrm{T}=\frac{2 \mathrm{u} \sin \theta}{\sigma}=6$ seconds

$4 \sin \theta=3 g \ldots \ldots(i)$

solve $(1)$ $\&(2)$ to get

$\tan \alpha=\frac{4 \sin \theta-g t}{4 \cos \theta}$

$\tan 30^{\circ}=\frac{4 \sin \theta-g \times 2}{4 \cos \theta}$

$\frac{1}{\sqrt{3}}=\frac{3 g-2 g}{4 \cos \theta}$

$4 \cos \theta=\sqrt{3} \mathrm{g}$ $…(2)$

Solve $(1)$ and $(2)$ to get

Standard 11

Physics

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