Question

A wooden block which is being acted upon by forces $F_1=10\text{N},F_2=2\text{N}$ is at rest on a rough horizontal plane as shown in figure. If force $F_1$ is removed, the resultant force acting on the block will be

• A. $2\text{N}$ towards left
• B. $2\text{N}$ towards right
• C. Zero
• D. Cannot be determined.

Answer 1

The correct option is C Zero

Given,
Force ($F_1)=10\text{N}$ acting towards right
Force ($F_2)=2\text{N}$ acting towards left



The net driving force on the block is $F$= $F_1-F_2=10-2=8\text{N}$ acting towards right.
Given that, the block is at rest $\therefore$ friction will be static in nature and acting towards left.
$\Rightarrow$Static frictional force ($f)=f_s=8\text{N}$


When $F_1$ is removed , only $F_2=2\text{N}$ is acting on the block towards left.
The block is at rest before $F_1$ is removed $\therefore$ the force acting on the block must be greater than the limiting frictional force for the block to move. But the applied force is $F_2=2\text{N}$ less than the static frictional force value$f=8\text{N}$
Hence the body is at rest and we can conclude from this fact that resultant force acting on the body is equal to zero.