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MHT CET 202626 AprilMorning Shift
Exam
MHT CET
Year
2026
Date
26 April
Shift
Morning Shift
Subject
Physics
Chapter
Thermal Properties of Matter

MHT CET 2026 · 26 April · Morning Shift · Physics · Thermal Properties of Matter

A cylindrical rod with one end in a steam chamber and the other end...

A cylindrical rod with one end in a steam chamber and the other end in ice results in melting of 0.10.1 gram of ice per second. If the rod is replaced by another with half the length and double the radius of the first, the thermal conductivity of the material of second rod is (14)th\left(\dfrac{1}{4}\right)^{th} that of first, the rate at which ice melts in gram per second will be (Latent heat of ice =80= 80 cal/g)

Options

  1. A3.23.2
  2. B1.61.6
  3. C0.20.2
  4. D0.10.1

Correct answer

C. 0.20.2

Step-by-step solution

The rate of heat flow through a rod is given by H=KAΔTLH = \dfrac{KA\Delta T}{L}.

The rate of melting of ice is m=HLf=KAΔTLLfm = \dfrac{H}{L_f} = \dfrac{KA\Delta T}{L L_f}, where LfL_f is the latent heat of fusion.

For the first rod, the rate of melting is:

m1=K1πr12ΔTL1Lf=0.1 g/sm_1 = \dfrac{K_1 \pi r_1^2 \Delta T}{L_1 L_f} = 0.1 \text{ g/s}

For the second rod, the given parameters are K2=K14K_2 = \dfrac{K_1}{4}, r2=2r1r_2 = 2r_1, and L2=L12L_2 = \dfrac{L_1}{2}.

The rate of melting for the second rod is:

m2=K2πr22ΔTL2Lfm_2 = \dfrac{K_2 \pi r_2^2 \Delta T}{L_2 L_f}

Substituting the values of K2K_2, r2r_2, and L2L_2:

m2=(K14)π(2r1)2ΔT(L12)Lfm_2 = \dfrac{\left(\dfrac{K_1}{4}\right) \pi (2r_1)^2 \Delta T}{\left(\dfrac{L_1}{2}\right) L_f}

m_2 = \dfrac{\left(\dfrac{K_1}{4}\right)^{4} \pi r_1^2 \Delta T}{\dfrac{L_1}{2} L_f}<br><br><br><br>m_2 = \dfrac{K_1 \pi r_1^2 \Delta T}{\dfrac{L_1}{2} L_f} = 2 \left( \dfrac{K_1 \pi r_1^2 \Delta T}{L_1 L_f} \right)

m2=2m1m_2 = 2 m_1

m2=2m_2 = 2\times0.1 = 0.2 \text{ g/s}

Answer: 0.2
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