After a supernova explosion, the remains of the stellar core ________
A) will always be a neutron star
B) may be either a neutron star or a black hole
C) will always be a black hole
D) may be either a white dwarf, neutron star, or black hole
B
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The heat conduction equation in cylindrical coordinates is
(a) Simplify this equation by eliminating terms equal to zero for the case of steady-state heat flow
without sources or sinks around a right-angle corner such as the one in the accompanying
sketch. It may be assumed that the corner extends to infinity in the direction perpendicular to
the page. (b) Solve the resulting equation for the temperature distribution by substituting the
boundary condition. (c) Determine the rate of heat flow from T1 to T2. Assume k = 1 W/(m K)
and unit depth .
GIVEN
• Steady state conditions
• Right-angle corner as shown below
• No sources or sinks
• Thermal conductivity (k) = 1 W/(m K)
FIND
(a) Simplified heat conduction equation (b) Solution for the temperature distribution (c) Rate of heat flow from T1 to T2 ASSUMPTIONS
• Corner extends to infinity perpendicular to the paper
• No heat transfer in the z direction
• Heat transfer through the insulation is negligible
SKETCH
Calculate the radius in nanometers of the orbit of a hydrogen atom's electron with n = 5
How many stars are there in our Solar System?
A. one B. nine C. a few hundred D. about ten million E. eight
Which of the following does not lend support to the idea that Pluto is a Kuiper-belt object?
A) Pluto has a cometlike composition and density. B) Pluto is regarded by many to be a planet. C) Some asteroids have their own moons. D) Pluto has a more eccentric orbit than other planets. E) Some known Kuiper-belt objects are hundreds of kilometers across.