Question

Statement (I) : Commerical airplanes save fuel by flying at higher altitudes during long trips. 

Statement (II) : At higher altitudes, the ambient temperature and the Carnot efficiency are low.

(a) Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I) 

(b) Both statement (I) and Statement (II) are individually true but Statement (II) is NOT the correct explanation of Statement (I) 

(c) Statement (I) is true but Statement (II) is false 

(d) Statement (I) is false but Statement (II) is true

Answer 1

(b) Both statement (I) and Statement (II) are individually true but Statement (II) is NOT the correct explanation of Statement (I) 

Both statement is correct. But statement II not explain the reason. At higher altitude the rate of decrease of thrust is less than the rate of decrease of density with altidue because some loss due reduced density is compensated by lesser drag. Due to considerable reduction in drag (at an altitude of 800 m, normal hight of commercial planes the drag is reduced than 25% of sea level drag) most of the commercial plane flying at high altidue.

At high altidue temperature decreases so, the cycle maximum temperature So, the cycle maximum temperature rise will decrease leads to decrease in carnot efficiency.