Approximately 80% of the energy used by the body must be dissipated thermally. The mechanisms available to eliminate this energy are radiati

Question

Approximately 80% of the energy used by the body must be dissipated thermally. The mechanisms available to eliminate this energy are radiation, evaporation of sweat, evaporation from the lungs, conduction, and convection. In this question, we will focus on the evaporation of sweat alone, although all of these mechanisms are needed to survive. The latent heat of vaporization of sweat at body temperature (37 °C) is 2.42 x 10^6 J/kg and the specific heat of a body is approximately 3500 J/(kg*°C).
(A) To cool the body of a jogger of mass 90 kg by 1.8°C , how much sweat has to evaporate?
O 130 g
O 230 g
O 23 g
O 13 g

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Gia Bảo 5 years 2021-07-24T00:04:28+00:00 1 Answers 63 views 0

Answers ( )

  1. diemthu
    0
    2021-07-24T00:05:42+00:00
    Reply

    Answer:

    the correct answer is c) 23 g

    Explanation:

    The heat lost by the runner has two parts: the heat absorbed by sweat in evaporation and the heat given off by the body

         Q_lost = – Q_absorbed

         

    The latent heat is

          Q_absorbed = m L

    The heat given by the body

          Q_lost = M c_{e} ΔT

           

    where m is the mass of sweat and M is the mass of the body

           m L = M c_{e} ΔT

            m = M c_{e} ΔT / L

    let’s replace

            m = 90  3.500  1.8 / 2.42 10⁶

     

            m = 0.2343 kg

    reduced to grams

            m = 0.2342 kg (1000g / 1kg)

            m = 23.42 g

     the correct answer is c) 23 g

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