If `vec F` is the force acting in a particle having position vector `vec r` and `vec tau` be the torque of this force about the origin, then

Options

A. `vec(r).vec(tau) =0 and vec(F). vec(tau)= 0`
B. `vec(r).vec(tau) = 0 and vec(F).vec(tau) ne 0`
C. `vec(r).vec(tau) ne 0 and vec(F).vec(tau)= 0`
D. `vec(r).vec(tau) ne 0 and vec(F).vec(tau) ne 0`

Answer

A

Explanation

`vec(tau)= vec(r) xx vec(F)` `vec(tau ) bot vec(r) and vec(tau) bot vec(F) " i.e. " vec(tau).vec(r)= 0 and vec(r) .vec(F)= 0`