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Physics 311, Quiz #14

Question 1: What are the units of thrust? 

  Answer:   Newtons  =  kg*m/s^2    (thrust is a force)

Question 2: The "mass ratio" of a rocket is the ratio of

  1. the molecular weights of the fuel and oxidizer
  2. the fuel mass to the payload mass
  3. the mass before the engines to the mass afterwards 
  Answer:  the mass before the engines to the mass afterwards

Question 3: Explain "escape velocity", using kinetic and gravitational potential energy. 

  Answer:   An object at the surface of some planet has
            smaller gravitational potential energy than 
	    it does far, far, above the surface of the planet.
	    If one gives that object the "escape velocity",
	    it will have just enough total energy (KE + GPE) 
	    to move an infinite distance away from the planet,
	    and end up with zero speed (and zero KE).

             on planet's surface               at infinite distance

	       GPE  +  KE             =            GPE   +  0

This page maintained by Michael Richmond. Last modified Feb 15, 2001.

Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.