Walker, Halliday & Resnick — Force and Motion-I: Problem 24

24 There are two horizontal forces on the 2.0 kg box in the overhead view of Fig. 5-28 but only one (of magnitude $F_1 = 30 \text{ N}$) is shown. The box moves along the $x$ axis. For each of the following values for the acceleration $a_x$ of the box, find the second force in unit-vector notation: (a) $10 \text{ m/s}^2$, (b) $20 \text{ m/s}^2$, (c) $0$, (d) $-10 \text{ m/s}^2$, and (e) $-20 \text{ m/s}^2$.