75. A mass m is attached to a spring which is held stretched a distance x by a force F, Fig. 6-45, and then released. The spring pulls the mass to the left, towards its natural equilibrium length. Assuming there is no friction, determine the speed of the mass m when the spring returns: (a) to its normal length (x = 0); (b) to half its original extension (x/2). m x = 0 FIGURE 6-45 Problem 75.