dynamics, check my ans
posted by jenny .
Three identical train locomotives, on separate tracks, apply the maximum force needed to begin moving. The first train consists of a single empty freight car, the second train consists of 50 empty freight cars, and the third train consists of 50 equally loaded freight cars. Rank the accelerations of the trains. All of the freight cars, when empty, are identical.
so the freight cars are 1 empty frieght car, 50 equally loaded freight cars, 50 empty frieght cars.
I have to rank the accelertion from large to small.
I think it's 1 empty car, 50 empty cars, and 50 equally loaded frieght car is the smallest.
am I right?

Right.
This follows from F=ma, or
a = F/m
When F is constant, then a is inversely proportional to m.
You have correctly ranked the three cases in the order of lightest to the heaviest loads.