Find the least horizontal force P to start motion of any part of the system of three blocks resting upon one another as shown in figure. The weights of the blocks are WA 300 N; WB = 100 N and Wc = 200 N. Between A and B, = 0.30 : between B and C, = 0.20; and between C and the ground, = 0.10. (a) 90 N (b) 80 N (c) 60 N (d) zero berth A B C P