Two blocks (M1 = 5kg and M2= 10kg) are pushed so that M1 is not touching the ground (in the air). The horizontal surface is frictionless but there is a friction between the two blocks (mu_k = .4 and mu_s = .5). Find the minimum force F needed so that M1 will remain "in the air" as the blocks move to the right. I drew free body diagrams for these. M1 has F pushing to the right, F_s along its vertical surface that touches M2, and M1*g pulling down. It also has a Normal force (N12) pushing left against it. M2 has a Normal force (N2) pushing up, M2*g pushing down, N12 pushing right against it. It also has F_s along its vertical surface that touches M1. I then use these relationships M1 x) F-N12=(M1+M2)a y) M1*g - F_s = 0 M2 x) F-N12 = (M1+M2)a y) N2-M2*g = 0 Are these correct so far? If yes, how do I find F from here not knowing "a"?