Many people will drink a cup of hot coffee (or maybe hot chocolate) on a cold da

Question

Many people will drink a cup of hot coffee (or maybe hot chocolate) on a cold day so that they feel "warmer". Calculate the change in body temperature for a "standard man" associated with rapidly drinking an 8 oz cup of coffee at a temperature of 80 degree C. How long would it take to obtain the same temperature change from the energy associated with the basal metabolism? Comment on whether you think having a hot drink really makes sense physically or whether this is primarily a psychological effect. Unlike people, the body temperature of a camel can vary by as much as 7 degree C over the course of the day, rising during the heat of the desert day and falling during the cool of the night. It is felt that these temperature swings are important in enabling the camel to conserve water in the hot dry desert climate. Explain (physically) how this temperature variation during the day allows the camel to conserve water. Estimate how much water a 500 kg camel could potentially save by allowing its temperature to vary by 7 degree C.

Explanation / Answer

1. (A) Suppose, a standard male weighs 80 kgs (2822 oz.). His body temperature is 37 degree Celsius. When drinking coffee, heat lost by the coffee will be gained by the man.

So, mcoffee x ccoffee x T= mman x cwater x Tman

So change in temperature of man= (mcoffee x ccoffee x T)/ (mman x cwater ) = {226.8 x 1.434 x (80-37)}/ {2822 x 4.2}= 13985/ 11852.4= 1.18 degree Celsius.

    (B) 1 cal= 4.2 joules. So, energy lost= 13985/ 4.2= 3329.8 cals. The average basal metabolic rate of a man is 1662 calories/ day. So 3329.8 cals will be lost in 24/ 1662 x 3329.8 = 48 hrs= 2 days

    (C) This sense is purely psychological as mass of coffee taken is very less.

2. (A) The rate of water lost due to dehydration of the camel is dependent on the temperature difference (temp. of camel body and outside temperature). By varying the temperature as much as 7 degree, this temperature difference is much reduced, and hence conservation of water is achieved.

    (B) If the water percentage of camel is 75 %, amount of water stored in a 500 kg camel is 500 x 0.75= 375 kgs. If the temperature did not vary, water lost would be 375 x cwater x T, and if temp varied by 7 degree, water lost would be 375 x cwater x (T- 7). So percentage saved= 7 %

Related Questions

Navigate

• Browse (All)
• Browse M
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.