A couple questions answered

Why are jet engines’ and rocket engines’ tails shaped differently, one gets narrower as the other gets wider?

The jet engine and the rocket engine have different nozzles because they are harnessing two different kinds of propulsion. The rocket engine is expelling burning gases out of the back, and these gases are still expanding when they are ejected. The open cone shaped nozzle allows the outward expansion of the hot gas to exert pressure on the rocket as it flies. The jet engine, by contrast, does all of it’s burning inside the engine. With the exception of afterburner, nothing is burning once it leaves the tailpipe of the jet. The constricting nozzles on the rear of a jet engine have much the same effect as putting a conical nozzle on a fireman’s hose – forcing the same volume through a smaller area must increase it’s speed, and therefore, allows the power of the engine to be more focused.
Learn more about rocket nozzle shapes here

Is the rotation of the earth considered the initial kinetic energy for a rocket before take-off?

Yes, a rocket sitting on its launching pad on Earth has an eastward velocity due to the rotation of the Earth. That is why almost all rockets take an easterly trajectory after a vertical launch. (Exceptions would be satellites designed to cover the largest portion of the Earth’s surface, placed in a polar orbit to allow the Earth to rotate beneath them.)

The maximum eastern velocity available is at the equator, where a point on the surface travels about 25,000 miles in 24 hours, or over 1000 miles per hour. As you move north or south of the equator, the circle traveled each day, and therefore the speed, becomes smaller until it becomes zero at the poles. This was a prime factor in locating Cape Canaveral as far south, in Florida, as it was. The velocity already imparted by Earth’s rotation is that much less needed by the rocket’s own fuel to attain the necessary orbital speed.

Interplanetary vehicles traveling to the outer planets can also take advantage of the Earth’s orbital velocity around the Sun (67,062 miles per hour), while those traveling to the inner planets must reduce the orbital speed imparted by the Earth to ‘fall’ toward a closer orbit.

More speed info: How fast is the Sun traveling in our arm of the Milky Way? 503,300 MPH or 225 KPS
read more here

Thanks to physlink.com

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