Q. A projectile is projected with $a$ speed $u$ making an angle $2\theta$ with the horizontal. What is the speed when its direction of motion makes an angle $\theta$ with the horizontal
A) $(u\cos{2\theta})/2$
B) $u\cos\theta$
C) $u(2\cos{\theta - \sec\theta})$
D) $u(\cos{\theta - \sec\theta})$
Explanation
(c) In projectile motion, horizontal component of velocity remains constant
$\therefore v\cos\theta = u\cos{2\theta}$
$\Rightarrow v = \frac{u\cos{2\theta}}{\cos\theta} = \frac{u(2\cos^{2}{\theta - 1})}{\cos\theta} = u(2\cos\theta - \sec\theta)$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.