CIEG 135
HOMEWORK #2
1) The most important part of this problem is to define the four steps (problem
definition, simplify, calculation and checking your estimation) in your answer. Each step
is evaluated as 1 point.
Our problem is to find out the number of tires sold annually in US.
Simplifications; The population of US is 300 million, and 2/3 of the population is older
than 16.
½ of the people who are older than 16 have a car.
You need to replace your tires in 3 years
Calculations: 300 000 000*2/3 = 200 000 000 people are older than 16.
200 000 000*1/2 = 100 000 000 cars owned in US
100 000 000 /3 = 33 000 000 cars need to change their tires.
1 car has 4 tires, so; 33 000 000*4 = 132 000 000 tires
Check; with safety factor and add the tire requirement for new cars
We can quess 175 000 000 tires in a year.
2) 1 gram salt is dissolved in 8-ounce tap water. Find the concentration of salt in mg/l
1 gr = 1000 mg
1 ounce = 0.0296 L
1 point
8 ounce = 0.2365882 L
1000 mg/ 0.2365882 L
1 point
conc = 4226.75 mg/L
1 point
Since we do not know the tap water, we can not be sure about the concentration. The tap
water might have salt in it or the salt we used might not be 100% pure salt (it might have
some water in it) 1 point
3) A wet sludge has 200 000 mg/L dry solids and 8000 mg/L zinc.
a) the conc of zinc as g Zn / g dry solids
8000 mg/ L= 8 g/L
2 points
200 000 mg/L = 200 g/L
8/200 = 0.04 g Zn / g dry solids
b)You might monitor the zinc content of soil, water resources periodically. You can run
tests on the caws (meat and milk) in order to see the level of zinc transferred to them.
2 points
4) Q = 60 gal/ min sediment load=2000 mg/L what is the sediment load in kg/day?
1 day = 24 hours
1 hour = 60 minutes
1 day = 60*24 = 1440 minutes
1 point
so Q = 60 gal/min * 1440 min/day = 86400 gal /day
1 gal = 3.7854 L
Q = 86400 gal/day * 3.7854 L/gal = 327 024 L/day
1 point
-3
Sediment load = 2 g/L = 2*10 kg/L
1 point
Sediment load = 2*10-3 kg/L * 372 059 L/day = 654.048 kg/day 1 point
5) conc = 120 lb fly ash/ hour
flow rate = 25 ft3/ sec
what is the conc of fly ash in μg/m3 ?
1 lb = 453.6 gr = 4536 * 105 μg
25 ft3/sec = 90000 ft3/hour
1 ft3 = 0.0283 m3
25 ft3/sec = 2547 m3/hour
120*453.6*106/2547 = 2.13 *107 μg/m3
1 point
1 point
1 point
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