Balancing forces application

A plank of mass $2 \text{ kg}$ and length $1 \text{ m}$ is placed on a horizontal floor. A small block of mass $1 \text{ kg}$ is placed on top of the plank, at its right extreme end. The coefficient of friction between plank and floor is $0.5$ and that between plank and block is $0.2$. If a horizontal force $=30 \text{ N}$ starts acting on the plank to the right, the time after which the block will fall off the plank is

Take $g=10 \text{ m/s}^{2}$