A block of mass m is kept on an another block of mass M. The coefficient of friction between the blocks varies as `mu=(mu_(0)+kx)` while friction between lower block and ground is zero. A time varying force F = 10t is applied horizontally on the upper block. Find time `t_(0)` when relative motion will start between the blocks. (x is relative displacement between the blocks.)

Answer

`(mu_(0)mg(M+m))/(10M)`