Question

A horizontal force of $10\text{N}$ is necessary to just hold a block stationary against a wall as shown in the figure. The weight of the block is $2\text{N}$. The coefficient of friction $\mu$, between the block and the wall is

• A. $0.30$
• B. $0.20$
• C. $0.25$
• D. $0.35$

Answer 1

The correct option is B $0.20$

Given, the weight of the block $W=2\text{N}$ and the applied external force to hold the block against wall $F=10\text{N}$
The FBD of the block can be shown as



From the FBD of the block we have normal force as:
$N_1=10\text{N}$
$f=\mu N_1=\mu \times 10=10\mu \text{N}$
Since, block is stationary with the wall, using $\Sigma F_y=0$, we get
$f-W=0\Rightarrow f=W\Rightarrow 10\mu =2$
$\Rightarrow \mu =\frac{2}{10}=0.2$