Questions 13 through 14 pertain to the situation described below: A 73.0-kg man is in an environment of –10.0°C. The temperature, area, and emissivity of his skin are 33.0°C, 1.73 m², and 0.820, respectively. Assume that his metabolic energy production is 211 J/s and his specific heat is 3.50 × 10³ J/(kg K). (13) What is the net emission power of his body? (A) 341 W; (B) 321 W; (C) 301 W; (D) 281 W; (E) 261 W. (14) What is the rate of his body temperature drop? (A) 2.39 °F/hr; (B) 2.59°F/hr; (C) 2.79°F/hr; (D) 2.99 °F/hr; (E) 3.19 °F/hr.
Energy transfer
The flow of energy from one region to another region is referred to as energy transfer. Since energy is quantitative; it must be transferred to a body or a material to work or to heat the system.
Molar Specific Heat
Heat capacity is the amount of heat energy absorbed or released by a chemical substance per the change in temperature of that substance. The change in heat is also called enthalpy. The SI unit of heat capacity is Joules per Kelvin, which is (J K-1)
Thermal Properties of Matter
Thermal energy is described as one of the form of heat energy which flows from one body of higher temperature to the other with the lower temperature when these two bodies are placed in contact to each other. Heat is described as the form of energy which is transferred between the two systems or in between the systems and their surrounding by the virtue of difference in temperature. Calorimetry is that branch of science which helps in measuring the changes which are taking place in the heat energy of a given body.
(13)
Given data
The mass of the man is m = 73 kg
The environment temperature is T = -10C
The temperature of the skin is Ts = 33C
The area of the skin is As = 1.73 m2
The emissivity of the skin is = 0.820
The metabolic energy production is E = 211 J/s = 211 W
The specific heat is C = 3.50 x 103 J/kgK
The expression for the net emission power of the body is given as:
Substitute the value in the above equation.
Thus, the net emission power emitted by the body is 321 W.
Thus, option (B) is correct.
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