1. Two forces, both in the r-y plane, act on a 1.5-kg mass, which accelerates at 7 3 m/s in a direction 30 counter-clockwise from the r-axis. One force has magnitude 6.8 N and points in the +x direction. Find the other force. FIGURE 6-59 Problem 3 Solution. Solution Newton's second law for this mass says Fret = F1 + F2 = ma, where we assume no other significant forces are acting. Since the acceleration and the first force are given, one can solve for the second, F, =ma