Question

A body is placed on a rough inclined plane of inclination $\theta$. As the angle \theta is the increased from $0^o$ to ${90}^o$, the contact force between the block and the plane :

• A. Remains constant
• B. First remains constant then decrease
• C. First decreases then increases
• D. First increases then decreases

Answer 1

The correct option is D First increases then decreases

Till $tan\theta <=\mu$

Friction force=$mgsin\theta$

$N=mgcos\theta$

Contact force =$\sqrt{N^2+f^2}=mg$

when $tan\theta >\mu$

$f=\mu N$

$N=mgcos\theta$

contact force will decrease as theta increases

So contact force between the block and the plane will first remain constant then decrease.