Two identical wooden blocks P and Q, each of mass 2\,kg, are arranged one over the other on a rough horizontal table. The coefficient of static friction between the two blocks is 0.40 while that between the lower block Q and the table is 0.30. A horizontal force F is applied to the lower block Q and is increased gradually from zero.
a. (i) Draw separate free-body diagrams for blocks P and Q naming every force acting on them.
b. (ii) Explain, with reasons, the condition under which the two blocks will move together without any slipping between them.
c. (iii) When F is increased slowly, predict which contact surface (P–Q or Q–table) will first reach its limiting value of static friction. Justify your answer qualitatively without using numerical calculations.