What is the first stage of planetary development?
a. cratering
b. flooding
c. bombardment
d. differentiation
e. slow surface evolution
d
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Organisms whose cells lack a nucleus are called
A) prokaryotes B) eukaryotes C) non-nucleotes D) karyokes
Which of these did Rutherford's "solar system" model of the atom successfully explain?
a. Spectral lines. b. The periodic properties of the elements. c. How atoms could give off light without collapsing. d. Why some alpha particles would bounce back when hitting an atom. e. Absorption spectra.
Air at 30°C enters a rectangular duct 1-m-long and 4 mm by 16 mm in cross-section at a rate of 0.0004 kg/s. If a uniform heat flux of 500 W/m2 is imposed on both of the long sides of the duct, calculate (a) the air outlet temperature (b) the average duct surface temperature, and (c) the pressure drop.
GIVEN
• Air flowing through a rectangular duct
• Inlet bulk air temperature (Tb,in) = 30°C
• Duct length (L) = 1 m
• Duct height (H) 4 mm = 0.004 m
• Duct width (w) = 16 mm = 0.016 m
• Air mass flow rate ( m ) = 0.0004 kg/s
• Uniform heat flux (q/A) = 500 W/m2 on the long sides
FIND
(a) Air outlet temperature (Tb,out)
(b) The average duct surface temperature (Ts)
(c) The pressure drop (? p)
ASSUMPTIONS
• The short sides of the duct are insulated
• Entrance effects are negligible
SKETCH
Because of trapped air inside, snow is a
A) poor conductor. B) good insulator. C) both of these D) none of the above