# Mechanical Engineering - Compressors, Gas Dynamics and Gas Turbines - Discussion

Discussion Forum : Compressors, Gas Dynamics and Gas Turbines - Section 1 (Q.No. 3)
3.
A rocket works with maximum overall efficiency when air-craft velocity is __________ the jet velocity.
equal to
one-half
double
Explanation:
No answer description is available. Let's discuss.
Discussion:
5 comments Page 1 of 1.

Rocket is a non air breathing engine, which doesn't depends on air.

It depends only on jet velocity. So jet velocity should be more than its aircraft velocity in this case.
(1)

According to kelvin planks statement we can't obtain the 100% efficiency. So we can't convert 100% work in another 100% work (i.e 100% velocity to another 100% velocity). It should be less then 100%.
(1)

Anuj said:   10 years ago
It should be equal to because for maximum efficiency the aircraft should move to its maximum velocity. As we know,

F = m*(vj-vi).

Aravindh.M said:   10 years ago
Sigma = u/cj;
For maximum sigma = 0.5, So 1/2.

Mahaboobbasha said:   8 years ago
Absolute velocity of a non-air breathing rocks jet velocity is always greater than its air jet velocity.