Chapter 4, Problem 3P

Two horizontal forces, ${\stackrel{\to }{F}}_1$ and ${\stackrel{\to }{F}}_2$ , are acting on a box, but only ${\stackrel{\to }{F}}_1$ is shown in the drawing. ${\stackrel{\to }{F}}_2$ can point either to the right or to the left. The box moves only along the $x$ axis. There is no friction between the box and the surface. Suppose that ${\stackrel{\to }{F}}_1=+9.0 \text{N}$ and the mass of the box is $3.0 \text{kg}$ . Find the magnitude and direction of ${\stackrel{\to }{F}}_2$ when the acceleration of the box is (a) $+5.0 \text{m}/{\text{s}}^2,$ (b) $-5.0 \text{m}/{\text{s}}^2,$ and (c) $0 \text{m}/{\text{s}}^2.$