Answer
a. Net force on each box, greatest to least: D, A=B=C
b. Acceleration of each box, greatest to least: A=C, B=D
Work Step by Step
Calculate the net force for each box, with forces to the right being positive and forces to the left being negative. Presented in the order ABCD, they are 5 N, 5 N, 5 N, 10 N.
Calculate the acceleration of each box from the net force.
$$a = F/m$$
The acceleration for each box, presented in the order ABCD, is $1 \frac{m}{s^{2}}$, $0.5 \frac{m}{s^{2}}$, $1 \frac{m}{s^{2}}$, $0.5 \frac{m}{s^{2}}$.
