Problem 3 (3.5 pts.). Two men are pushing a box of a mass M = 100 kg in opposite directions by applying forces F1 = 1300 N and F2 = 500 N, as is shown in Fig. 1 (a). There is also an unknown friction force f acting on the box. (a) Find the friction force f if the box moves with acceleration a = 0.5m/s2. (b) How will this acceleration change if another small box of mass m = 10 kg is placed on top of our box M, see Fig. 1 (b). Assume that the friction force remains the same when the other box m is added. Will this acceleration increase or decrease and why? M (b) F m F2 M Figure 1: Schematic graph for Problem 3