The mass of the Milky Way Galaxy can be estimated by:
A) the orbital motions of the stars within the galaxy.
B) the mass of the planets in the Solar System.
C) the luminosity of the stars of the neighboring galaxies.
D) the concept laid down by the spiral density wave theory.
A
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An object moving with speed 
collides head-on with an object at rest that is very much more massive. If the collision is elastic, how does the lighter object’s speed 
after collision compare to ?
A. 
B. 
C. 
D. 
E. 
F. 
A beam of electrons moves at velocity 
. The number of particles per unit volume in the beam of area A is ?. If we imagine a cylindrical Gaussian surface of radius r and length 
centered on the beam, the electron flux through the surface is
A.
B.
C.
D.
).E.
).What happens to the temperature of a substance while it is changing state?
Stern and Gerlach performed an experiment that showed the space quantization of silver atoms in an inhomogeneous magnetic field. Their experiment demonstrated that