A horizontal force F acts on the block of mass m and the block remains stationary, if we pull the block by the force F making an angle $\mathrm{\theta }$ and the block remains stationary, the value of friction force is

 

 

• A

  $\mathrm{\mu } \mathrm{mg}$

• B

  $\mathrm{F} \cos \mathrm{\theta }$

• C

  $\frac{\mathrm{\mu mg}}{\sin \mathrm{\theta }+\mathrm{\mu } \cos \mathrm{\theta }}$

• D

  $\frac{\mathrm{\mu mg}}{\sqrt{1+{\mathrm{\mu }}^2}}$