If we compress 4.5 billion years into a calendar year, humans make their mark on the calendar
A) the very last minute of New Years Eve.
B) on December 25th.
C) at 12:00 pm, December 30th.
D) at 11:50 pm, December 31st.
Answer: D
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Conservation of Momentum: The momentum of an isolated system is conserved
A. only in inelastic collisions. B. only in elastic collisions. C. in both elastic and inelastic collisions.
What do we mean by a "super Earth"?
A) a planet made of metal and rock that is larger in mass than Earth B) a planet that is more massive than Earth and also has surface oceans C) a planet with an Earth-like orbit that has more abundant life than Earth D) a planet similar in size to Earth but orbiting close to its star
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
Parallax would be easier to measure if
a. Earth's orbit was larger. b. the stars were farther away. c. Earth moved faster along its orbit. d. all of these e. none of these