Question

A projectile is fired with a speed $u$ at an angle $\theta$ with the horizontal. Its speed when its direction of motion makes an angle $\alpha$ with the horizontal is

• A. $u\sec \theta \cos \alpha$
• B. $u\sec \theta \sin \alpha$
• C. $u\cos \theta \sec \alpha$
• D. $u\sin \theta \sec \alpha$

Answer 1

The correct option is C $u\cos \theta \sec \alpha$


Let $v$ be the speed of projectile when its direction of motion makes an angle $\alpha$ with horizontal.
As the horizontal component of velocity remains constant during projectile motion.
$\Rightarrow v\cos \alpha =u\cos \theta$
$\Rightarrow v=u\cos \theta \sec \alpha$