Question

In a figure shown below, the work done by force of friction on the block is

• A. Zero
• B. Positive
• C. Negative
• D. cannot be determined

Answer 1

The correct option is A Zero

Given, mass of block $\left(m\right)=5\text{kg}$
Applied force $\left(F\right)=40\text{N}$
By the FBD of the block:

$R=5g=50\text{N}$

$(f_s{)}_{\text{max}}={\mu }_{s}R=0.8\times 50=40\text{N}$

Since the external force and frictional force are equal and opposite, the body is at rest.
There is no displacement of the block.
The work done by force of friction is zero. ($\Rightarrow W=fs=0$)

Hence option A is correct.