Question

A block rests on a rough inclined plane making an angle ${30}^0$ with horizontal. The coefficient of static friction between the block and inclined plane is $0.8$. If the maximum frictional force on the block is $10N$, the mass of the block in $kg$ is ($g=10m/s^2$):

• A. 1.44
• B. 4
• C. 1.6
• D. 2.5

Answer 1

The correct option is A 1.44

From FBD of block, we can see that frictional force, $f=mg\cos \theta \mu =mg\cos {30}^0\times 0.8=mg\left(\frac{\sqrt{3}}{2}\right)\times 0.8=10N$
$m=\frac{10\times 2}{0.8\times 10\times \sqrt{3}}=1.44kg$