A projectile is thrown with some initial velocity at an angle α to horizontal. Its velocity when it

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3-2.Motion in Plane

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A projectile is thrown with some initial velocity at an angle $\alpha$ to the horizontal. Its velocity when it is at the highest point is $(2 / 5)^{1 / 2}$ times the velocity when it is at height half of the maximum height. Find the angle of projection $\alpha$ with the horizontal.

A

$30$

B

$45$

C

$60$

D

$37$

Solution

(c)

$(u \cos \alpha)=\sqrt{\frac{2}{5}} \sqrt{\left(u \cos \alpha^2\right)+\left\{(u \sin \alpha)^2-2 g h\right\}}$

Here, $h=\frac{H}{2}=\frac{u^2 \sin ^2 \alpha}{4 g}$

Solving this equation, we get $\alpha=60^{\circ}$

Standard 11

Physics

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