Elizabeth lifts a 10 N book from the floor to the table, a height of 2 m. How much work does Elizabeth do?
A) 20 watts
B) 5 joules
C) 20 joules
D) Elizabeth does zero work
E) 5 watts
C
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Conduction: The thermal conductivity of a certain concrete is 0.80 W/m . K and the thermal conductivity of a certain wood is 0.10 W/m ? K. How thick would a solid concrete wall have to be in order to have the same rate of heat flow through it as an 8.0-cm thick wall made of solid wood? Both walls have the same surface area and the same temperature difference across their faces.
A. 53 cm B. 64 cm C. 71 cm D. 85 cm
Pulsars are thought to be
A) accreting white dwarfs. B) rapidly rotating neutron stars. C) unstable high-mass stars. D) accreting black holes.
If you sit in a boat near the edge of a river channel, you might notice the water moving more quickly on the side away from the shore (the channel side). If you are initially moving with the river, you will be pushed
A. into the channel by the turbulent flow of the water. B. toward the shore because the water flow is laminar around the boat. C. toward the shore because the water pressure is smaller on the shore side. D. into the channel because the water pressure is larger on the shore side.
A turbine blade 6.3-cm-long, with cross-sectional area A = 4.6 x 10–4 m2 and perimeter P = 0.12 m, is made of stainless steel (k = 18 W/(m K). The temperature of the root, Ts, is 482°C. The blade is exposed to a hot gas at 871°C, and the heat transfer coefficient h? is 454 W/(m2 K). Determine the temperature of the blade tip and the rate of heat flow at the root of the blade. Assume that the tip is insulated.
GIVEN
FIND
ASSUMPTIONS
Steady state conditions prevail
The thermal conductivity is uniform
The tip is insulated
The cross-section of the blade is uniform
One dimensional conduction
SKETCH
