A block of mass $10 \mathrm{kg}$ is released on rough incline plane. Block start descending with acceleration $2 \mathrm{m} {\mathrm{s}}^{-2}.$ Kinetic friction force acting on block is $\left(\mathrm{take} \mathrm{g}=10 \mathrm{m} {\mathrm{s}}^{-2}\right)$

A block of mass $10 \mathrm{kg}$ is kept on a fixed rough $(\mu =0.8)$ inclined plane of angle of inclination $30°.$ The frictional force acting on the block is

A block of mass $10 \mathrm{kg},$ moving with acceleration $2 \mathrm{m} {\mathrm{s}}^{-2}$ on horizontal rough surface is shown in figure

The value of coefficient of kinetic friction is