Question

5. Read the passage given below :
1. The scientist Hero of Alexandria built a small jet engine in about 60 A.D. It was powered by steam
escaping from a hollow sphere through two nozzles that pointed in opposite directions
. The escaping
steam turned the sphere in much the same manner as a jet of water spins a rotating lawn sprinkler.
2. The growing tensions that led to World-War-II (1939-1945) accelerated the development of jet engines
to propel aircraft
. The first flight of a jet aeroplane occurred in Germany in 1939: A turbo jet designed
by Hans Joachim Von Ohian, a German physicist powered this aeroplane, the Heinkel He 178. In Italy,
the jet propelled Caproni-Campini CC2 aeroplane, was built and flown in 1940. Neither of these first
two jet aircraft engines proved practical. A more successful turbo jet was soon developed by Sir Frank
Whittle, an officer in Great Britain's royal air force. Whittle's turbo jet powered the Gloster E 28/39,
which first flew in 1941.
3. Jet propulsion is the production of motion in one direction by releasing a highpressure stream of
gas
in the opposite direction. Rockets, guided missiles and many other aeroplanes are powered by jet
propulsion. How is this done?
4. A jet propulsion plant is used for the propulsion of aircraft and other missiles by the reaction of a jet
of gases that are discharged with a high velocity. The mass and velocity of the jet is obtained from
the combustion of liquid fuels. If the propulsion unit contains its own oxygen supply for combustion
purposes, the system is called “rocket propulsion” and is used to propel rockets out of the orbit of the
earth. In this case the jet contains exhaust gases only, and is produced directly by combustion processes
without the use of mechanical contrivances. The term “jet propulsion” is used when the
oxygen is
obtained from surrounding atmosphere.
5. At low altitudes the efficiency of the screw propeller may be as high as 85%, but it decreases with increase
of altitude; at very high altitudes, where the exceedingly rarefied the atmosphere is the efficiency reduces.
This demerit can be overcome by using jet propulsion at higher altitudes. A jet propulsion plant has a
relatively low overall efficiency but it increases at higher altitudes, because although the propulsive force
tends to decrease with decrease in atmospheric density, this is more than balanced by the consequent
increase of speed. Jet propulsion is less proficient than the propeller at low and medium altitudes, but
has higher efficiency at very high altitudes.
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Answer 1

Answer:

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