The rate of cratering in the lunar highlands shows us that
A) they must be younger than the older, darker mare.
B) most of the asteroids must have hit the Moon, not the Earth.
C) they range from 4.6 - 4.4 billion years old, on average.
D) the largest impacts are the youngest, such as Copernicus and Tycho.
E) the oldest rocks are at least as old as the mare, but some craters are much younger.
C
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A long, half-round cylinder is placed in an air stream with its flat face down-stream. An electrical resistance heater inside the cylinder maintains the cylinder surface temperature at 50°C. The cylinder diameter is 5 cm, the air velocity is 31.8 m/s, and the air temperature is 20°C. Determine the power input of the heater per unit length of cylinder. Neglect radiation heat transfer.
GIVEN
• A long, half-round cylinder in an air stream with its flat surface downstream
• Cylinder surface temperature (Ts) = 50°C
• Cylinder diameter (D) = 5 cm = 0.05 m
• Air velocity (U?) = 31.8 m/s
• Air temperature (T?) = 20°C FIND
• Power input to the heater ( Q G/L)
ASSUMPTIONS
• Steady state
• Radiative heat transfer is negligible
• Flow separates at the cylinder edges as shown below
SKETCH
The mirrors for X-ray telescopes are the same shape as those of optical reflectors
Indicate whether the statement is true or false
Which of the following statements is(are) correct when an ideal gas goes from an initial to a final state in a single process?
a. No work is done on or by the gas when the volume remains constant. b. No energy is transferred into or out of the gas as heat transfer when the temperature remains constant. c. The internal energy of the gas does not change when the pressure remains constant. d. All the statements above are correct. e. Only statements (a) and (b) above are correct.
A thin layer of oil floats on a water puddle. An observer sees a colored pattern. This happens because
A. water transmits light and never reflects light. B. sunlight's frequency range shifts to infrared at the boundary of water and oil. C. two surfaces each transmit some light and reflect some light. D. oil always does this, even if it is not on water.