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Question 6 (a) Why is it necessary to balance rotors? What is a "rigid rotor"? Can rigid rotors be balanced at any speed? If not, why not? (6 marks) A (b) A shaft carries three pulleys, each of mass 12 kg. in planes A, B and C, the eccentricity of the mass centres of these pulleys being 5 mm, 4 mm and 3 mm respectively. The bearings are positioned in planes L and M. The relative axial positions of these planes are shown in Figure 6 (a), and the relative angular positions of the mass centre of each of the pulleys are indicated in Figure 6 (b). The shaft rotates at 1000 rad/s. Determine the dynamic force exerted by this shaft on each of the bearings. 100 mm 100 mm 240° B Be 200 mm 90° Figure Q6 a and be 100 mm M (14 marks)