Static friction between two surfaces

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

A particle of mass $2 \mathrm{kg}$ is moving in circular path with constant speed $20 \mathrm{m} {\mathrm{s}}^{-1}.$ The magnitude of change in velocity when particle travels from $A$ to $P$ will be