The position vector vec$(r)$ of a particle relative to a certain point has a magnitude of $3$ m $,$ and the force vec$(F)$ on the particle has a magnitude of $4$ N $.$

Part $1$

$($a$)$ What is the angle between the directions of vec$(r)$ and vec$(F)$ if the magnitude of the associated torque equals $0N*m?$

$0$

Greater than $0$ but less than $90$

$90$

Greater than $90$ but less than $180$

$180$