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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Heat Transfer

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Heat Transfer

A steel rod ( K = 46 J s^ -1 m^ -1 ^ ^ ^ ^ -1 ) of length 1.0 m has...

A steel rod (K = 46 \text{ J s}^{-1} \text{ m}^{-1} ^{}^{{}^{\circ}}\textC^{-1}) of length 1.0 m1.0 \text{ m} has one end kept in ice at 0^{}^{{}^{\circ}}\text{C} and the opposite end in boiling water at 100^{}^{{}^{\circ}}\text{C}. The rod has a cross-sectional area of 0.04 cm20.04 \text{ cm}^2. Assuming there is no heat loss to the surrounding atmosphere, determine the mass of ice melting per second. The latent heat of fusion of ice is 3.36×105 J kg−13.36 \times 10^5 \text{ J kg}^{-1}.

Options

  1. A5.5×10−8 g s−15.5 \times 10^{-8} \text{ g s}^{-1}
  2. B1.8×10−2 g s−11.8 \times 10^{-2} \text{ g s}^{-1}
  3. C5.5×10−5 g s−15.5 \times 10^{-5} \text{ g s}^{-1}
  4. D5.5×10−2 g s−15.5 \times 10^{-2} \text{ g s}^{-1}

Correct answer

C. 5.5×10−5 g s−15.5 \times 10^{-5} \text{ g s}^{-1}

Step-by-step solution

The rate of heat transfer through the rod is given by Fourier's law of heat conduction:

H=KA(T1−T2)LH = \dfrac{KA(T_1 - T_2)}{L}

Substituting the given values:
K = 46 \text{ J s}^{-1} \text{ m}^{-1} ^{}^{{}^{\circ}}\textC^{-1}
A=0.04 cm2=4×10−6 m2A = 0.04 \text{ cm}^2 = 4 \times 10^{-6} \text{ m}^2
T_1 - T_2 = 100^{}^{{}^{\circ}}\text{C} - 0^{}^{{}^{\circ}}\text{C} = 100^{}^{{}^{\circ}}\text{C}
L=1.0 mL = 1.0 \text{ m}

H=46×4×10−6×1001.0=1.84×10−2 J s−1H = \dfrac{46 \times 4 \times 10^{-6} \times 100}{1.0} = 1.84 \times 10^{-2} \text{ J s}^{-1}

The heat transferred per second is used to melt the ice. The mass of ice melting per second mm is given by:

m=HLfm = \dfrac{H}{L_f}

Given the latent heat of fusion of ice Lf=3.36×105 J kg−1L_f = 3.36 \times 10^5 \text{ J kg}^{-1}:

m=1.84×10−23.36×105 kg s−1m = \dfrac{1.84 \times 10^{-2}}{3.36 \times 10^5} \text{ kg s}^{-1}

m≈5.476×10−8 kg s−1m \approx 5.476 \times 10^{-8} \text{ kg s}^{-1}

Converting the mass to grams per second:

m=5.476×10−8×103 g s−1≈5.5×10−5 g s−1m = 5.476 \times 10^{-8} \times 10^3 \text{ g s}^{-1} \approx 5.5 \times 10^{-5} \text{ g s}^{-1}
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