For a given element, which of the following has the greatest entropy?
(a) A perfect single crystal
(b) A polycrystal
(c) A liquid
(d) A vapor
(d) A vapor
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Photos A and B both show the same field of view containing a star-forming molecular cloud. One of the photos was taken in visible light and the other in infrared light. Which one is the visible-light photo, and how do you know?
A) Photo A is the visible-light photo, and we can tell because dust in the molecular cloud absorbs visible light, making the cloud appear dark. B) Photo A is the visible-light photo because its stars are more colorful. C) Photo B is the visible-light photo because more stars are visible in the molecular cloud. D) Photo B is the visible-light photo because the molecular cloud has a reddish tint.
The nucleus of an ordinary hydrogen atom consists of a(n) ______________
Fill in the blank(s) with correct word
A stainless steel pin fin 5-cm-long, 6-mm-OD, extends from a flat plate into a 175 m/s air stream as shown in the sketch. Estimate (a) the average heat transfer coefficient between air and the fin. (b) the temperature at the end of the fin. (c) the rate of heat flow from the fin with glycerol at 20°C flowing over the fin at 2 m/s. The plate temperature is 50°C.
GIVEN
• A stainless steel pin fin in an air stream
• Pin length (L) = 5 cm = 0.05 m
• Pin diameter (D) = 6 mm = 0.006 m
• Glycerol velocity (U?) = 2 m/s
• Glycerol temperature (T?) = 20°C
• Plate temperature (Tp) = 50°C FIND
(a) The average heat transfer coefficient ( h c) (b) The temperature of the end of the fin (TL) (c) The rate of heat flow from the fin (qf) ASSUMPTIONS
• Steady state
• Turbulence in the glycerol approaching the fin is low
• Radiative heat transfer is negligible
• Steel is type 304
• Steel properties are uniform
• Variation of the thermal properties of glycerol and steel with temperature is negligible
PROPERTIES AND CONSTANTS
Thermal conductivity (k) = 0.285 W/(m K) Kinematic viscosity (?) = 1175 × 10–6 m2/s Prandtl number (Pr) = 12,609 for type 304 stainless steel ks = 14.4 W/(m K) at 20°C
A 30.0-kg child sits on one end of a long uniform beam having a mass of 20.0 kg, and a 40.0-kg child sits on the other end
The beam balances when a fulcrum is placed below the beam a distance 1.10 m from the 30.0-kg child. How long is the beam? A) 2.12 m B) 1.98 m C) 1.93 m D) 2.07 m E) 2.20 m