If the force is always perpendicular to motion, then KE remains constant

If force is always parallel to motion

No work is done by a force on an object if a) the force is always perpendicular to its velocity b) the force is always perpendicular to its acceleration .c) the object is stationary but the point of application of the force moves on the object d) the object moves in such a way that the point of application of the force remains fixed.

In a projectile motion the velocity a) is always perpendicular to the acceleration b) is not always perpendicular to the acceleration c) is perpendicular to the acceleration for one instant only d) is perpendicular to the acceleration for two instants.

Name the force which always opposes motion.

In a projectile motion the velocity (a) is always perpendicular to the acceleration (b) is not always perpendicular to the acceleration (c) is perpendicular to the acceleration for one instant only (d) is perpendicular to the acceleration for two instants.