Determine the number of air masses through which the sun’s rays must pass to reach the earth at the equator and at the equinox.
What will be an ideal response?
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Quasars are isolated supermassive black holes, and not associated with galaxies
a. True b. False Indicate whether the statement is true or false
For the following situations consider moving a positive charge from very far away to the origin along the y-axis. For which situation would you do the most work?
1.A
2.B
3.C
4.D
5.A & C
6.None of the above.
7.Cannot be determined
Significant Figures: What is 
expressed to the correct number of significant figures?
A. 0.91 B. 0.911 C. 0.9108 D. 0.9
An automotive catalytic convertor is a packed bed in which a platinum catalyst is coated on the surface of small alumina spheres. A metal container holds the catalyst pellets and allows engine exhaust gases to flow through the bed of pellets. The catalyst must be heated by the exhaust gases to 300°C before the catalyst helps combust unburned hydrocarbons in the gases. The time required to achieve this temperature is critical because unburned hydrocarbons emitted by the vehicle during a cold start comprise a large fraction of the total emissions from the vehicle during an emission test. A fixed volume of catalyst is required but the shape of the bed can be modified to increase the heat-up rate. Compare the heat-up time for a bed 5-cm-diameter and 20-cm-long with one 10 cm diameter and
5-cm-long. The catalyst pellets are spherical, 5-mm-diameter, have a density of 2 g/cm3, thermal conductivity of 12 W/(m K) and specific heat of 1100 J/(kg K). The packed-bed void fraction is 0.5. Exhaust gas from the engine is at a temperature of 400°C, a flow rate of 6.4 gm/s, and has the properties of air.
GIVEN
FIND
The heat-up time (t) for the pellet surface temperature (Tp) to reach 300°C
ASSUMPTIONS
The initial temperature of the bed (To) = 20°C
SKETCH
