Question

In a projectile motion the velocity

• A. is always perpendicular to the acceleration
• B. is never perpendicular to the acceleration
• C. is perpendicular to the acceleration for one instant only
• D. is perpendicular to the acceleration for two instants.

Answer 1

The correct option is C is perpendicular to the acceleration for one instant only

Projectile motion has 2 compounds horizontal & vertical $\mu \sin \theta \&\mu \cos \theta$ (4 is the initial velocity). Acceleration is only vertical in projectile motions.

So there is always some angle between velocity of acceleration. But at the

top most point of flight, only $\mu \cos \theta$ (horizontal) in present but acceleration (g) in vertical, just st one instant.