9. A small block of mass m = 10 kg rests on top of a large block of mass M = 40 kg. There is friction between the small block and the large block and the large block slides with negligible friction on a flat horizontal surface. A force F = 148 N is applied to the large block causing both blocks to accelerate to the right with acceleration a as shown. If the force F is increased slightly, the small block will slide off of the large block. What is the coefficient of static friction z, between the small and large block? A) u =020 B) 4 =030 C) u =040 D) u =050 E) 4 =060