Rocket engines work by throwing matter out the back end of a rocket as fast as they can. Usually this matter is in the form of gas. This causes the rocket to move forward in the opposite direction from the ejected matter, thanks to Newton’s Third Law of Motion which says that ‘For every Action, there is an equal and opposite Reaction’.
To lift tons of cargo into space, rocket engines have to be very powerful. Engineers usually compare different engines by their thrust and by their specific impulse. This makes it easy to decide which kind of engine to use to put different payloads into space in the most efficient and low-cost way possible.
Problem 1
– Specific Impulse Isp = V/g is the ratio of the exhaust speed of the engine (V) divided by the acceleration of gravity at Earth’s surface (g), where g is 9.8 meters/sec2 and V is measured in meters/sec. The J-2X rocket engine has an Isp=421 seconds.
How fast are the exhaust gases leaving the bottom of the engine in
A) kilometers/sec?
B) feet per second?
C) miles per hour?
(1 kilometer = 3280 feet; 1 mile = 5280 feet)
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