Question

The elevator shown in the figure is descending with an acceleration of $2m/s^2$. The mass of the block $A=0.5\text{kg}$. The force exerted by the block $A$ on the block $B$ is (take $g=10{\text{m/s}}^2$)

• A. $2\text{N}$
• B. $4\text{N}$
• C. $6\text{N}$
• D. $8\text{N}$

Answer 1

The correct option is B $4\text{N}$

Let $A$ applies a force $R$ on $B$, then $B$ also applies an opposite and equal force $R$ on $A$.
The FBDs of the block are as shown

Considering the frame of reference as elevator, a pseudoforce $ma$ will be acting on A upwards where $m$ is mass of block A, therefore
$mg-R=ma$
$\Rightarrow R=m(g-a)=0.5[10-2]=4\text{N}$