Two discs of mass 2 kg and 3 kg of radius 1 m and 2 m respectively placed together are rotated about an axis through their common centre as shown in figure. Find the net moment of inertia of the system about given axis.
A
6 kg-m2
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B
5 kg-m2
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C
1 kg-m2
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D
7 kg-m2
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Solution
The correct option is D7 kg-m2 Given:
Mass of disc 1, m1=2 kg having radius r1=1 m
Mass of disc 2, m2=3 kg having radius r2=2 m.
Moment of inertia of disc of mass 2 kgI1=m1r212 =2×122=1 kg-m2
Moment of inertia of disc of mass 3 kg, I2=m2r222 =3×222=6 kg-m2
Net moment of inertia of both discs about given axis Inet=I1+I2=(1+6) kg-m2 =7 kg-m2