Question

# A circular disc is rotating about its own axis. An external opposing torque of magnitude 0.02Nm is applied on the disc, due to which it comes to rest in 5 seconds. The initial angular momentum of the disc is:

A
0.1 kgm2s1
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B
0.04 kgm2s1
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C
0.025 kgm2s1
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D
0.01 kgm2s1
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Solution

## The correct option is A 0.1 kgm2s−1¯C=0.02N/mt=5sectorque is applied for 5sec and torque is rate of change of angular momentum so,angular momentum lost due to decelaration =¯C×△t=(0.02)×5=0.1change in angular momentum = final angular momentum − initial angular momentum0.1=0− Initial angular momentum∴ Initial angular momentum = 0.1 kg m2/s

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