A crossbar fixture holding four balls are initially (t = 0) moving with velocity v before being subjected to a moment M = (0.25t + 1.6) lb- ft. Neglect the size of the balls and the weight of the fixture. Assume all balls weigh 6 lb. M (a) Calculate the initial speed of the balls v [ft/s] if after 4 seconds their velocity v = 2v. Use angular impulse-momentum. (b) Suppose now that two of the balls weigh 6 lb and the other two weigh 12 lb. Determine the time t [sec] it takes for the balls to move from V = 10 ft/s to v = 15 ft/s. Use the same moment function M and angular impulse-momentum. (c) (Concept) If angular momentum is constant, does this also mean that linear momentum is constant? Explain why or why not? 0.6 ft