1. The problem statement, all variables and given/known data A train consists of a 4000 kg locomotive pulling two loaded boxcars, the ﬁrst with a mass of 12,000 kg and the second with a mass of 16,000 kg. Assume that the boxcar wheels roll without friction and ignore aerodynamics. The acceleration of the train is 0.4 m/s2. With what force strength, in Newtons, does the ﬁrst boxcar pull on the last boxcar? 2. Relevant equations F=ma 3. The attempt at a solution I thought the mass should be the total of the last two boxcars which would be 12000 plus 16,000 =28,000 so I tried 28,000*0.4m/s^2 which came out to 11,200 which is obviously wrong the answer to the question should be 6E3, what am I doing wrong?