Question

A block rests on a rough inclined plane making an angle of $30^\circ $ with the horizontal. The coefficient of static friction between the block and the plane is $0.8$ . If the frictional force on the block is $10 \, N$ , the mass of the block is $\left(T a k e \, g = 10 \, m \, s^{- 2}\right)$

• A. $1 \, kg$
• B. $2 \, kg$
• C. $3 \, kg$
• D. $4 \, kg$

Answer 1

Answer: (B)

As the block is at the state of rest,
$\therefore R=mgcos \theta $ , which is balanced.
and $f_{1}= \, $ force of friction $ \, =10 \, N \, $ (given)

Hence, $f_{1}=mgsin \theta $
$10=m\times 10\times sin 30^{o}$
$m=\frac{10}{10 \times sin 30^{o}}=2 \, kg$