Four shopping carts are interlocked, so each cart pushes the next. Cart 1 has mass m1 = 439 kg, cart 2 has mass m2 = 214 kg, cart 3 has mass m3 = 195 kg and cart 4 has mass m4 = 269. A supermarket employee pushes cart 1 (with mass m1) horizontally with a force of magnitude F = 851 N. Assume there is no friction anywhere.
a) Find the magnitude of the acceleration of the carts.
b) Find the magnitude of the force exerted by cart 3 on cart 4.