You would expect to find the least number of fossils in rocks from the
A) Cenozoic era.
B) Mesozoic era.
C) Paleozoic era.
D) Precambrian era.
Answer: D
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Causing an object to start moving on a frictional surface requires
A. less force than is needed to keep it moving on the surface. B. the same force as is needed to keep it moving on the surface. C. more force than is needed to keep it moving on the surface. D. a force equal to the weight of the object. E. a force opposite to the normal force.
If you are measuring the thickness of a strand of human hair, the most appropriate SI unit is the
A) kilometer. B) meter. C) centimeter. D) millimeter. E) micrometer.
Optical interferometry is more in use than radio interferometry
Indicate whether the statement is true or false
To measure thermal conductivity, two similar 1-cm-thick specimens are placed in an apparatus shown in the accompanying sketch. Electric current is supplied to the 6-cm by 6-cm guarded heater, and a wattmeter shows that the power dissipation is 10 watts (W). Thermocouples attached to the warmer and to the cooler surfaces show temperatures of 322 and 300 K, respectively. Calculate the thermal conductivity of the material at the mean temperature in W/(m K).
GIVEN
Thermal conductivity measurement apparatus with two samples as shown
Sample thickness (L) = 1 cm = 0.01 cm
Area = 6 cm ? 6 cm = 36 cm2 = 0.0036 m2
Power dissipation rate of the heater (qh) = 10 W
Surface temperatures
Thot = 322 K
Tcold = 300 K
FIND
The thermal conductivity of the sample at the mean temperature in W/(m K)
ASSUMPTIONS
One dimensional, steady state conduction
No heat loss from the edges of the apparatus
SKETCH
