Question

A body of mass $m$ is kept on a rough fixed inclined plane of angle of inclination $\theta$. It remains stationary. Then magnitude of force acting on the body by the inclined plane is equal to

• A. mg
• B. mg sin $\theta$
• C. mg cos $\theta$
• D. none

Answer 1

The correct option is A mg

Friction force by the inclined plane is $=\mu mg\cos \theta =mgsin\theta$ up the inclined plane since the block does not slide.

Normal force perpendicular to inclined plane is $mgcos\theta$.

So, Total force is vector sum of two forces is equal to $mg$.
$N=mgcos\theta$, $f_s=mgsin\theta$
$R^2=N^2+f_s^2\Rightarrow R=mg$