A block of mass $40 \mathrm{kg}$ slides over a surface, when a mass of $4 \mathrm{kg}$ is suspended through an inextensible massless string passing over frictionless pulley as shown below.
The coefficient of kinetic friction between the surface and block is $0.02$. The acceleration of block is: (Given $g=10{ \mathrm{m} \mathrm{s}}^{-2}$.)

• Correct answer
  A

  $\frac{8}{11} \mathrm{m} {\mathrm{s}}^{-2}$
• B

  $1 \mathrm{m} {\mathrm{s}}^{-2}$
• C

  $\frac{1}{5} \mathrm{m} {\mathrm{s}}^{-2}$
• D

  $\frac{4}{5} \mathrm{m} {\mathrm{s}}^{-2}$

Hence, the correct answer is option: 'A'.