What is the critical temperature for stage 7; why?
What will be an ideal response?
The core must reach 15 million degrees K for the outward pressure generated by hydrogen fusion to balance the inward pull of gravity.
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Based on Mercury's peak temperature of about 700 K, what would the average molecular speed of carbon dioxide be? How does this compare to Mercury's escape velocity? If Mercury's atmosphere initially had substantial carbon dioxide, in line with what
is believed about the early atmospheres of the other terrestrial planets, do you think Mercury would have retained this atmosphere? Why/why not? Would your answer change if you considered only Mercury's coldest regions that are around 125 K?
Which of the following is not a phase of the Moon?
A) first-quarter moon B) third-quarter moon C) half moon D) full moon E) new moon
An electronic circuit board is the shape of a flat plate 0.3 m × 0.3 m in plan-form and dissipates 15 W. It is placed in operation on an insulated surface in a horizontal position or at an angle of 45 degrees to horizontal, in both cases; it is in still air at 25°C. If the circuit fails above 60°C, determine if the two proposed installations are safe.
GIVEN
• A flat plate with insulated back, horizontal or at an angle of 45 degrees in still air
• Plate size (s × s) = 0.3 m × 0.3m
• Heat generation rate (qG) = 15 W
• Air temperature (T?) = 25°C
• Maximum plate temperature (Ts) = 60°C
FIND
• If the two plate positions are safe
ASSUMPTIONS
• Radiative heat transfer is negligible
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 43°C
Thermal expansion coefficient (?) = 0.00316 1/K
Thermal conductivity (k) = 0.0267 W/(m K)
Kinematic viscosity (?) = 17.9 × 10–6 m2/s
Prandtl number (Pr) = 0.71
Two important properties of young neutron stars are
A) extremely rapid rotation and a weak magnetic field. B) extremely slow rotation and a strong magnetic field. C) extremely rapid rotation and a strong magnetic field. D) no rotation and a weak magnetic field. E) no rotation and no magnetic field.