A block P of mass is placed on a horizontal frictionless plane. A second block of same mass is placed on it and is connected to a spring of spring constant , the two blocks are pulled by distance . Block oscillates without slipping. What is the maximum value of frictional force between the two blocks [2004]

(1)
Here acceleration is same for both and as block oscillates but does not slip. The system oscillates with angular frequency . The spring is stretched by .
Angular frequency of the system,
Maximum acceleration of the system in SHM
This acceleration to the lower block is provided by friction
Maximum force of friction