The torsional spring is untwisted when the slender uniform rod is in the vertical position. The rod has a length of 0.79 m and a mass of 4.4 kg. The rod is released from rest in the horizontal position shown. What should the stiffness K of the spring be so that the rod will have an angular speed of  = 3.5 rad/s when it passes the vertical position? The rod rotates freely about the fixed pin support at O. The motion occurs in a vertical plane. Choose the correct answer. a) 21.8 N.m/rad b) 17.9 N.m/rad c) 19.5 N.m/rad d) 18.4 N.m/rad e) 20.2 N.m/rad

The torsional spring is untwisted when the slender uniform rod is in the vertical position. The rod has a length of 0.79 m and a mass of 4.4 kg. The rod is released from rest in the horizontal position shown. What should the stiffness K of the spring be so that the rod will have an angular speed of  = 3.5 rad/s when it passes the vertical position? The rod rotates freely about the fixed pin support at O. The motion occurs in a vertical plane. Choose the correct answer.