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JEE Main201912 Apr 2019Morning ShiftPhysicsThermal Properties of MatterActual

At 40 ° C , a brass wire of 1 m m 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 40 ° C to 20 ° C 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 m s - 2 )

Options

  1. A0.9 k g
  2. B0.5 k g
  3. C1.5 k g
  4. D9 k g

Correct answer

D. 9 k g

Step-by-step solution

M g = A Y l Δ l Δ l l = α Δ T M g = A Y α Δ T M = A Y α Δ T g = π × 0.001 2 × 10 11 × 10 - 5 × 20 10 = 2 π Closest value of M is 9 kg.

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