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43. The radius of gyration of a uniform rod of length l, about an axis passing through a point l/4 away from the centre of the rod, and perpendicular to it, is:

1. l/4
2. l/8
3. √(7/48) l
4. √(3/8) l

Correct answer: √(7/48) l

Solution

By parallel axis, I = (1/12) m l^2 + m (l/4)^2 = m l^2 (1/12 + 1/16) = 7 m l^2 / 48. Radius of gyration k = sqrt(I/m) = sqrt(7/48) l.

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