Question

A body is uniformly rotating about an axis fixed in an inertial frame of reference. Let A be a unit vector along the axis of rotation and B be the unit vector along the resultant force on a particle P of the body away from the axis. The value of A.B is

(a) 1
(b) -1
(c) 0
(d) None of these.

Answer 1

Answer ⇒ Option (c) . 0

Explanation ⇒ According to the question, the body is uniformly rotating thus the resultant force on the particle P will be in the radial direction.

∴ The directions of A and B will be perpendicular to each other.

Mathematically,

Angle between them = θ = 90°

∴ A.B = |A|.|B|. Cos90° [A.B. is the dot product of vectors.]

= |A|.|B|. 0

= 0

Hence, the answer is Option (c).

Hope it helps.