The bright O and B tracers make the spiral arms of galaxies, including ours, appear to be _____
A) yellow
B) blue
C) orange
D) red
B
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What causes the geological activity seen on some of the inner moons of Jupiter?
a. Constant collisions with space debris provide a power source for geological activity. b. The strong magnetic field of Jupiter heats the surface of the inner moons. c. Tidal friction as a result of being so close Jupiter heats their interiors. d. Solar radiation reflected of Jupiter's surface provides a power source for geological activity.
Suppose that you are inside a smooth-flying [no bumps] jet plane that is speeding up along a straight line
Can you detect this acceleration without directly or indirectly making use of anything outside of your own reference frame? If so, how could you observe this; and if not, why not? A) No, because of the principle of relativity. B) No, because of the principle of the constancy of lightspeed. C) No, because jet planes move far too slowly for such an effect to actually be observed. D) Yes. For example, if you dropped a coin you would find that it lands to the front of the drop point. E) Yes. For example, if you dropped a coin you would find that it lands to the rear of the drop point.
Calculate the overall heat transfer coefficient and the rate of heat flow from the hot gasses to the cold air in the cross flow tube-bank of heat exchanger shown in the accompanying illustration for the following operating conditions
Air flow rate = 0.4 kg/s.
Hot gas flow rate = 0.65 kg/s.
Temperature of hot gasses entering exchanger = 870°C.
Temperature of cold air entering exchanger = 40°C.
Both gases are approximately at atmospheric pressure.
GIVEN
? The crossflow tube bank heat exchanger shown above
? Air flow rate
( ma ) = 0.4 kg/s
? Gas flow rate
( mg) = 0.65 kg/s
? Entrance temperatures
? Air (Ta,in) = 40°C
? Gas (Tg,in) = 870°C
? Both gases are at 1 atm pressure
FIND
(a) The overall heat transfer coefficient
(b) The rate of heat transfer (q)
ASSUMPTIONS
? The hot gases have the same thermal properties as air
? No scaling
? Thermal resistance of the tube walls can be neglected
PROPERTIES AND CONSTANTS
From Appendix 2, Table 28, for dry air at the entering temperatures
Liquid water cannot survive on the surface of Mars because:
A) the atmosphere is too dense. B) the air pressure is too low. C) Mars has the highest escape velocity. D) Mars has never differentiated.