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3-2.Motion in Plane
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A stone is projected from the ground with velocity $25\,m/s$. Two seconds later, it just clears a wall $5 \,m$ high. The angle of projection of the stone is ........ $^o$ $(g = 10m/{\sec ^2})$
A
${30}$
B
${45}$
C
${50.2}$
D
${60}$
Solution
(a) For vertical upward motion $h = ut – \frac{1}{2}g{t^2}$
$5 = (25\sin \theta ) \times 2 – \frac{1}{2} \times 10 \times {(2)^2}$
$⇒$ $25 = 50 \sin \theta $
$⇒$ $\sin \theta = \frac{1}{2}$
$⇒$ $\theta = 30^\circ $
Standard 11
Physics