What would you expect to be different in a planetary system in which the nebular gas is blown into interstellar space by a stellar wind earlier than occurred in our solar system?
A) No terrestrial planets would form.
B) Jovian planets would be less massive because they had less time to gather hydrogen and helium gas.
C) All planets would be more massive than Jupiter.
D) Most of the planets would be destroyed by migration onto the central star.
B) Jovian planets would be less massive because they had less time to gather hydrogen and helium gas.
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Who first noticed that for Cepheid variable stars, there was a direct relation between the luminosity and the period of the variation in their brightness?
a. Henrietta Leavitt b. Edwin Hubble c. John Glenn d. Carl Sagan e. Annie Cannon
The surfaces of two concentric spheres having radii of 75 and 100 mm are maintained at 325 K and 275 K, respectively.
(a) If the space between the spheres is filled with nitrogen at 500 kPa, estimate the
convection heat transfer rate.
(b) If both sphere surfaces are black, estimate the total rate of heat transfer between them.
(c) Suggest ways to reduce the heat transfer.
GIVEN
? Concentric spheres with nitrogen between them
? Nitrogen pressure (p) = 500 kPa
? Sphere radii
? Inner sphere (ri) = 75 mm = 0.075 m
? Outer sphere (ro) = 100 mm = 0.1 m
? Sphere temperatures
? Inner sphere (Ti) = 325 K
? Outer sphere (To) = 275 K
? Both spheres are black
FIND
(a) Convective heat transfer (qc)
(b) Total heat transfer (qtotal)
(c) Suggest ways to reduce the heat transfer
ASSUMPTIONS
? Sphere temperatures are constant and uniform
? Only the density of the nitrogen is affected significantly by pressure
? The nitrogen behaves as an ideal gas
PROPERTIES AND CONSTANTS
From Appendix 2, Table 33, for Nitrogen at atmospheric pressure and the mean temperature of 300 K
The density of the nitrogen at 500 kPa can be calculated from the ideal gas law
Does an electric field exert a force on a beam of moving electrons? Assume the motion of the electrons is along the x axis and field is in the y direction
1.yes 2.no
A ball rolls off the edge of a table. The horizontal component of the ball's velocity remains constant during its entire trajectory because
A) the ball is not acted upon by any force. B) the net force acting on the ball is zero. C) the ball is not acted upon by a force in the horizontal direction. D) the ball is not acted upon by a force in the vertical direction. E) None of the other choices is correct.