If the presently accepted value of ?o = 0.3 (excluding dark energy) is indeed correct, then the universe will:
A) expand forever.
B) expand to the critical size for the Steady State model, then become static.
C) stop expanding in about forty billion years, to collapse into the next cosmic cycle.
D) Two of the answers are correct.
E) All of the above are correct.
A
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A boat floating in a large pool is loaded with wood blocks. The water level at the pool's edge is marked with a red line. The blocks are now thrown overboard and float outside the boat. When the water becomes calm again,
A. the red line is slightly higher than the water level. B. the red line is still at the water level. C. the red line is slightly lower than the water level.
Calculate the maximum safe heat flux in the nucleate-boiling regime for water flowing at a velocity of 15 m/s through a 1.2-cm-ID tube 0.31-m-long if the water enters at 100 kPa pressure and 100°C saturated liquid.
GIVEN
? Nucleate boiling of water flowing through a tube
? Water velocity (V) = 15 m/s
? Tube inside diameter (D) = 1.2 cm = 0.012 m
? Tube length (L) = 0.31 m
? Water pressure (p) = 1 atm
? Water temperature (Tw) = 100°C
FIND
? The maximum safe heat flux in the nucleate boiling regime (q?max)
ASSUMPTIONS
? Steady state
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 13, for water at 100°C, 1 atm
From Appendix 2, Table 35, for steam at 100°C: ?v = 0.5977 kg/m3
From Table 9.2: Surface tension at 100°C (s) = 0.0589 N/m
From Table 9.1: For water on copper, Csf = 0.0130
Flowing water erodes stream channels by
A) chemical weathering. B) hydraulic action and abrasion. C) chemical weathering, hydraulic action, and abrasion. D) channel erosion and abrasion.