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Units And Measurement

Question
CBSEENPH11017588

Calculate the radius of gyration of hollow sphere about its diameter and tangent.


Solution

Let M be the mass and R be the radius of hollow sphere.

(i) Radius of gyration about diameter:

Moment of inertia of hollow sphere about diameter is, 
                 straight I equals 2 over 3 MR squared
If Kd is radius of gyration about diameter then,

space space space space space space space space M K subscript straight d squared equals 2 over 3 M R squared
rightwards double arrow space space space space space space space straight K subscript straight d equals square root of 2 over 3 end root straight R

(ii) Radius of gyration about tangent:

Moment of inertia of hollow sphere about tangent can be calculated by using the theorem of parallel axis.
That is, 
           straight I subscript 1 equals straight I subscript straight d plus MR squared equals 2 over 3 MR squared plus MR squared equals 5 over 3 MR squared
If Kt is radius of gyration about tangent then,
MK subscript straight t squared equals 5 over 3 MR squared

space space space space space straight K subscript straight t equals square root of 5 over 3 end root straight R subscript 0