JEE PYQ: Thermal Properties Of Matter Question 14
Question 14 - 2019 (12 Apr 2019 Shift 1)
At 40°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 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; $g = 10$ ms$^{-2}$)
(1) 9 kg
(2) 0.5 kg
(3) 1.5 kg
(4) 6.28 kg
Show Answer
Answer: (4)
Solution
$L\alpha\Delta T = \frac{FL}{AY}$, so $F = A Y \alpha \Delta T = \pi \times 10^{-6} \times 10^{11} \times 10^{-5} \times 20 = 20\pi$ N. $M = \frac{F}{g} = 2\pi = 6.28$ kg
BETA
