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At 40º C, a brass wire of 1 mm radius is hung from the ceiling. A small mass, M is hung from the free end of the wire. When the wire is cooled down from 40ºC to 20ºC it regains its original length of 0.2 m. The value of M is close to : (Coefficient of linear expansion and Young’s modulus of brass are 10 –5 /°C and 10 11 N/m 2 , respectively; g= 10 ms –2 )

1. 1.5 kg
2. 0.5 kg
3. 9 kg
4. 0.9 kg

Correct answer: 9 kg

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