A m = 2.0-kg block sits on a M = 4.0-kg block. There is no friction between m and M. There is no friction between M and the surface below it. If F = 12 N, which blocks move and what is their acceleration?
(1) M moves with a = 3.0 m/s2
(2) m and M move with a = 2.0 m/s2
(3) m moves with a = 6.0 m/s2
(4) M moves with a = 2.0 m/s2
(5) None of these.