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3-2.Motion in Plane
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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
$T=6 s$
$\frac{24 \sin \theta}{g}=6$
$u \sin \theta=3 g$
$u \sin \theta=3 g$
$u \cos \theta=\sqrt{3 g}$
$\tan \alpha=\frac{u \sin \theta g t}{u \cos \theta}$
$\tan 30^{\circ}=\frac{3 g-g \cdot 2}{u \cos \theta}$
$u \cos \theta=\sqrt{3} g$
$\therefore \theta=60^{\circ}$
$\mathrm{u}=20 \sqrt{3} \mathrm{m} / \mathrm{s}$
Standard 11
Physics
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