The Sahara is one of the hottest places on Earth. A man lost his way in this big desert. He accidentally spilled all of his water from his watr bottle on the ground. Before the incident, the bottle contained 2 litres of water. (Density of water= 1g cm^-3 )
a) Suppose the sun gives heat to the water on the ground at a power of 2kW. How long will it take for all the spilled water to evaporate?(Initial temperature of the water is 30℃). Give your answer to the nearest minute.
Answer: 2260s=38mnutes
b) it may be fatal for a man to lose 5 litres of water without replenishing fresh water. Will the man die if he stays in the Sahara for 2 hours without intaking any water?
Answer:∵mass of sweat lost in 2 hours ∴ he will not die
How can i get the answer? Thanks!
Physic Questions
2009-12-14 2:07 am
回答 (2)
2009-12-14 6:38 am
✔ 最佳答案
(a) Heat required to evapourates 2 L (i.e. 2000 g = 2 kg) of water= (2 x 4200 x (100-30) + 2 x 2.27 x 10^6) J = 5.13 x 10^6 J
hence time taken = 5.13x10^6/2000 s = 2564 s
(b) Heat absorbed by the man from the sun in 2 hours = 2000 x (2 x 3600) J
= 1.44 x 10^7 J
Mass of water evapourated = (1.44x10^7/5.13x10^6) x 2 kg = 2.81 kg
The water lost from the man in 2 hours is less than 5 litres (= 5 kg), henc the man will not die.
2009-12-15 2:13 am
無最佳解答
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