1. A uniform rod of mass m = 1 kg and length 1 = 0.25 m (Figure QB1.1) is supported by a pin joint at A and a spring with stiffness k = 300 N/m at B. The mass moment of inertia of the rod about point A is: ml 3 JA = The beam is given a small rotation and vibrates freely. Assume the angular rotation (8) about point A, is small and that the positive direction is clockwise. B A 1 Figure QB1.1 a. Write the force in the spring at B as a function of angular displacement 8. [4 marks] b. Write the equation of motion for small vibrations about point A [6 marks]