question_answer

A spool is pulled at an angle of \[\theta \]with the horizontal on a rough horizontal surface as shown in the figure. If the spool remains at rest, then the angle \[\theta \] is equal to

A) \[30{}^\circ \]                   

B) \[60{}^\circ \]                   

C) \[45{}^\circ \]                   

D) \[75{}^\circ \]

Correct Answer: B

Solution :

[b] Net torque about \[P=0\] \[F\cos \theta (2R-R\,cos\theta )=F\sin \theta \,R\sin \theta \] \[2\cos \theta =1\] \[\Rightarrow \,\,\,\theta =60{}^\circ \]