D -175 mm 125 min B A Sample Problem 12.9 A 0.5-kg collar is attached to a spring and slides without friction along a circular rod in a vertical plane. The spring has an unde- formed length of 150 mm and a constant k = 200 N/m. Knowing that the collar has a speed of 3 m/s as it passes through point B, determine the tangential acceleration of the collar and the force of the rod on the collar at this instant. STRATEGY: This problem deals with forces and accelerations, so you need to use Newton's second law. The collar moves along a curved path, so you should use normal and tangential coordinates. (continued)