The H-R diagram main-sequence of stars has a limit at the lower-mass or energy-output end because
a. low-mass stars form from the interstellar medium very rarely.
b. low-mass objects are composed primarily of solids, not gases.
c. pressure does not depend on temperature in degenerate matter.
d. the lower limit represents when the radius of the star would be zero.
e. there is a minimum temperature for hydrogen nuclear fusion (the definition of a star).
e
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A stepped steel shaft (G 5 75 GPa) with diameters d1 5 36 mm and d2 5 32 mm is twisted by torques T at each end. Segment lengths are L1 5 0.9 m and L2 5 0.75 m. If the allowable shear stress is 28 MPa and maximum allowable twist is 1.8°, the maximum permissible torque is approximately:
(A) 142 N?m
(B) 180 N?m
(C) 185 N?m
(D) 257 N?m
Which technology can allow a single ground-based telescope to achieve images as sharp as those from the Hubble Space Telescope?
A. adaptive optics B. grazing incidence C. interferometry
What is the density of a mixture of 85% air 
and 15% water vapor (density of water vapor 
A. 1.70 
B. 1.87
C. 1.05
D. 1.11
E. 1.19
Under what circumstances will a nova occur?
What will be an ideal response?