Practice Question 3 A toy train is pulled across a table as shown above . Neglecting any internal frictions, if T1 = 12 N and the mass of the flat car is 2.0 kg and the caboose is 6.0 kg, what is (a) the acceleration of the system; (b) the net force on the caboose; (c) the tension in T2? (How is this question related to Newton's 3 rd Law?) (a) Consider the flat car and the caboose together a "system." a ( system) F net (system ) 12 N : 1.5 m m (system) (2.0kg +6.0kg) (b) Fnet (caboose)=ma=(6.0 kg) (1.5 2)=9.0 N (c) Since there is only one unbalanced force acting on the caboose, the tension T2 T2=F net =9.0 N How is this question is related to Newton's 3"d Law? The tension that pulls the caboose forward is equal in magnitude but opposite in direction to the tension pulling backward on the flat car. You could also find the tension T2 by considering the net force on the flat car: F net ( flat car)=ma=(2.0kg) (1.5 2)=3.0N , So 12N-T2=3.0N - 12=9.0N