The efficiency of a Carnot engine is 35.0%. What is the temperature of the cold reservoir if the temperature of the hot reservoir is 500 K?
A)
95.0 K
B)
175 K
C)
325 K
D)
269 K
E)
231 K
C
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If the angular size of a spherical object is known, along with its distance from Earth, what third quantity can be determined?
A) the object's brightness B) the object's mass C) the baseline D) the object's diameter
A heat exchanger wall consists of a copper plate 2 cm thick. The heat transfer coefficients on the two sides of the plate are 2700 and 7000 W/( m2 K), corresponding to fluid temperatures of 92 and 32°C, respectively. Assuming that the thermal conductivity of the wall is 375 W/ ( m K), (a) compute the surface temperatures in °C, and (b) calculate the heat flux in W/ m2.
GIVEN
• Heat exchanger wall, thickness (L) = 2 cm = 0.02 m
• Heat transfer coefficients
? hc1 = 2700 W/(m2 K)
? hc2 = 7000 W/(m2 K)
• Fluid temperatures
? Tf1 = 92°C
? Tf2 = 32°C
• Thermal conductivity of the wall (k) = 375 W/( m K) FIND (a) Surface temperatures (Tw1, Tw1) in °F (b) The heat flux (q/A) in W/m2. ASSUMPTIONS
• One dimensional heat transfer prevails
• The system has reached steady state
• Radiative heat transfer is negligible
SKETCH
An astronaut in a space suit is motionless in outer space. The propulsion unit strapped to her back ejects some gas with a velocity of 40.0 m/s. The astronaut recoils with a velocity of 1.00 m/s. If the mass of the astronaut and space suit after the gas is ejected is 100 kg and the mass of the gas ejected is 2.50 kg, then the total kinetic energy after the ejection of the gas is
A. 2,050 J. B. 3,430 J. C. 4,150 J. D. 5,070 J. E. 6,320 J.
When you see your shadow on a sunny day, it has a fuzzy edge. This is
A. an example of diffraction. B. not caused by diffraction because the wavelength of visible light is too small to produce visible diffraction around a person. C. not caused by diffraction because diffraction only occurs for openings, not objects blocking light. D. not caused by diffraction because there are too many wavelengths in sunlight to see the effect.