Question

A block $‘A^{\prime }$ of mass $45\text{kg}$ is placed on a block $‘B^{\prime }$ of mass $123\text{kg}$. Now block $‘B^{\prime }$ is displaced by external agent by $50\text{cm}$ horizontally towards right. During the same time block $‘A^{\prime }$ just reaches to the left end of block $B$. Initial position is shown in figure. Refer to the figure and find the work done (in $\text{Nm}$) by frictional force on block $A$ in ground frame during above time. (take $g=10m{s}^{-2}$)

Answer 1

Displacement of $A$ w.r.t. ground $=20\text{cm}$
towards right
Friction force on $A=0.2\times 45\times 10=90\text{N}$ towards right
$W_{fr}=90\times \frac{20}{100}=18\text{Nm}$