Consider the following statements regarding performance of turbojet engines
1. The thrust decreases, at higher altitude due to reduced density of air and consequently lower mass flow of air.
2. At subsonic speeds, the effect of increased velocity is to increase the air flow and the thrust increases
3. The relative velocity of jet with respect to the medium decreases at higher speeds which tends to reduce the thrust
4. For turbojet engine the thrust of. jet at subsonic speeds remains relatively constants
Which of the statements given above are correct?
a. 1, 2, 3 and 4 b. 1 and 3
c. 1, 2 and 4 d. 2, 3 and 4