Question

A massless string and a spring connect two blocks $A$ and $B$ to each other. Block $B$ slides over a frictionless inclined plane while block A slides over horizontal surface. Coefficient of friction between block A horizontal surface is $\mu =\mathrm{0.2.}$ At the instant shown blocks are moving with constant speed. Mass of block $A$ and energy stored in spring are respectively. $\left[g=10m/s^2,m_B=2kg\right]$

• A. $5kg,1J$
• B. $10kg,0.05J$
• C. $5kg,0.05J$
• D. $10kg,1J$

Answer 1

Answer: (C)

$2g\sin \theta =kx=\mu m_{A}g$
$\Rightarrow m_A=\frac{2g\sin \theta }{\mu g}=\frac{2\sin \theta }{\mu }=\frac{2\times \frac{1}{2}}{0.2}=5kg$
$kx=2\times 10\times \frac{1}{2}=10$
$x=\frac{10}{1\times 10^3}=1cm$
$\Rightarrow$ Energy $=\frac{1}{2}\times 10^3\times {\left(10^{-2}\right)}^2=0.05$ Joule