Q. If F⃗ is the force acting on a particle having position vector r⃗ and τ⃗ be the torque of this force about the origin, then:
A) r⃗ · τ⃗ > 0 and F⃗ · τ⃗ < 0
B) r⃗ · τ⃗ = 0 and F⃗ · τ⃗ = 0
C) r⃗ · τ⃗ = 0 and F⃗ · τ⃗ ≠ 0
D) r⃗ · τ⃗ ≠ 0 and F⃗ · τ⃗ = 0
Explanation
[Solution from source] τ⃗ = r⃗ × F⃗ is perpendicular to the plane containing r⃗ and F⃗. A vector perpendicular to both has zero dot product with each, so r⃗ · τ⃗ = 0 and F⃗ · τ⃗ = 0. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.