Four blocks of the same material, m1, m2, m3 and m4 have masses 2 kg, 4 kg, 2.5 kg and 2 kg respectively. All of them have equal surface area in contact with the concrete surface over which they are kept. Let the frictional force acting on them be F1, F2, F3 and F4 respectively.
The correct order of friction force acting on them when they slide is: