The shaft of a small turbine with a single disc is found to have a static deflection of 0.355 mm. Find the critical speed of the shaft-disc system and calculate percentage change in the diameter of the shaft that will be required to raise the critical speed to 2100 rpm. If the initial displacement of the centre of the mass of the disc from the axis of shaft is 0.5 mm, compare the deflection of the shaft at 1500 rpm in the two cases.