Is space expanding within clusters of galaxies? Why or why not?
A) no, because their gravity is strong enough to hold them together even while the universe as a whole expands
B) no, because the universe is not old enough yet for these objects to have begun their expansion
C) no, because expansion of the universe affects only empty space, not space in which matter is present
D) Yes, and that is why clusters tend to grow in size with time.
A) no, because their gravity is strong enough to hold them together even while the universe as a whole expands
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A cylinder contains 13 moles of an ideal gas at a temperature of 300 K. The gas is compressed at constant pressure until the final volume equal 0.70 times the initial volume
The molar heat capacity at constant volume of the gas is 24.0 J/mol ? K. What is the change in the internal (thermal) energy of the gas during this process? (R = 8.31 J/mol ? K) A) -28 kJ B) -38 kJ C) 28 kJ D) 38 kJ E) -9.7 kJ
A diver shines an underwater searchlight at the surface of a pond (n = 1.33). At what angle (relative to the surface) will the light be totally reflected?
A. 47.3° B. 41.2° C. 51.1° D. 58.7° E. 49.8°
Samples of the Earth's molten outer core come directly through the mantle, pour out of volcanoes, and can be studied in labs
Indicate whether the statement is true or false
The temperature of air flowing through a 25-cm-diameter duct whose inner walls are at 320°C is to be measured with a thermocouple soldered in a cylindrical steel wall of 1.2-cm-OD with an oxidized exterior, as shown in the accompanying sketch. The air flows normal to the cylinder at a mass velocity of 17,600 kg/(h m2). If the temperature indicated by the thermocouple is 200°C, estimate the actual temperature of the air.
GIVEN
• Cylindrical thermocouple wall in an air duct
• Duct diameter (Dd) = 25 cm = 0.25 m
• Duct wall temperature (Tds) = 320°C =m 593 K
• Wall outside diameter (Dw) = 1.2 cm = 0.012 m
• Exterior of wall is oxidized
• Air mass velocity /m A
= 17,600 kg/(h m2)
• Thermocouple indicated temperature (Ttc) = 200°C = 473 K
FIND
• Air temperature (T?) ASSUMPTIONS
• Steady state
• Thermal resistance between the thermocouple and the wall exterior surface is negligible
• Inside of duct behaves as a black body enclosure
• Conduction to the thermocouple wall from the duct wall can be neglected
PROPERTIES AND CONSTANTS
the emissivity of oxidized steel (?) = 0.94. From Appendix 1, Table 5, the Stephan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4)