Consider methods to identify the major polluters from among the many cars on the road (a few are responsible for most of the pollution). List as many as you can and explain how they can help reduce the problem
How many of these do you know are being used in your state?
By eye: Observation of plumes of smoke from the tailpipe. By nose: Recognizing
the acrid smell of burnt oil, the stink of NOx, and unburned hydrocarbons (the other gases
are relatively lacking in smell). By instrument: Many states have inspection stations that
motorists must visit every year to catch major polluters, but conditions of the test are not
always the same as driving conditions. Mobile detectors would be more effective, but are
expensive and they require someone to drive them who is able to give a summons and make
it stick. Students will undoubtedly come up with more suggestions than are listed here.
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Somewhere between the Earth and the Moon is a point where the gravitational attraction of the Earth is canceled by the gravitational pull of the Moon. The mass of the Moon is 1/81 that of the Earth. How far from the center of the Earth is this point?
a. 8/9 the way to the Moon b. 9/10 the way to the Moon c. 3/4 the way to the Moon d. 80/81 the way to the Moon
If there were no air resistance and no gravity:
a. an object thrown at an angle upward would come down, but more slowly than it does on Earth. b. an object thrown at an angle upward would eventually change direction to move at constant height, rather than up. c. an object thrown at an angle upward would come down the same way it does on Earth. d. an object thrown at an angle upward would slow down and stop. e. an object thrown at an angle upward would keep going up in the same direction for ever and never come down.
It's the June solstice, the Sun is at your zenith, and you have a UT clock that tells you it is midnight in Greenwich, England. Where are you?
A) on the Tropic of Cancer near the International Date Line B) on the equator near the International Date Line C) on the Tropic of Cancer, due south of Greenwich, England D) at latitude 25°S and longitude 49°E
A salesperson for insulation material claims that insulating exposed steam pipes in the basement of a large hotel will be cost effective. Suppose saturated steam at 5.7 bars flows through a 30-cm- OD steel pipe with a 3 cm wall thickness. The pipe is surrounded by air at 20°C. The convective heat transfer coefficient on the outer surface of the pipe is estimated to be 25 W/(m2 K). The cost of generating steam is estimated to be $5 per 109 J and the salesman offers to install a 5 cm thick layer of 85% magnesia insulation on the pipes for $200/m or a 10-cm-thick layer for $300/m. Estimate the payback time for these two alternatives assuming that the steam line operates all year long and make a recommendation to the hotel owner. Assume that the surface of the pipe as well as the
insulation have a low emissivity and radiative heat transfer is negligible.
GIVEN
Steam pipe in a hotel basement
Pipe outside diameter (Do) = 30 cm = 0.3 m
Pipe wall thickness (Ls) = 3 cm = 0.03 m
Surrounding air temperature (T?) = 20°C
Convective heat transfer coefficient (hc) = 25 W/(m2 K)
Cost of steam = $5/109J
Insulation is 85% magnesia
FIND
Payback time for
(a) Insulation thickness (LIa) = 5 cm = 0.05 m; Cost = $200/m
(b) Insulation thickness (LIb) = 10 cm = 0.10 m; Cost = $300/m
Make a recommendation to the hotel owner.
ASSUMPTIONS
The pipe and insulation are black (? = 1.0) The convective resistance on the inside of the pipe is negligible, therefore the inside pipe surface temperature
is equal to the steam temperature The pipe is made of 1% carbon steel Constant thermal conductivities
SKETCH
