Rotational MotionHard

Question

Two point masses of 0.3 kg and 0.7 kg are fixed at the ends of a rod of length 1.4 m and of negligible mass. The rod is set rotating about an axis perpendicular to its length with a uniform angular speed. The point on the rod through which the axis should pass in order that the work required for rotation of the rod is minimum, is located at a distance of : -

Options

A.0.42 m from mass of 0.3 kg
B.0.70 m from mass of 0.7 kg
C.0.98 m from mass of 0.3 kg
D.0.98 m from mass of 0.7 kg

Solution

Work required is minimum for rotation when the MI is minimum. It is minimum about that axis which pass through CM & perpendicular to the plane.
                          
C.M. from 0.3kg mass = = 0.98

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