truck capacity

[Isabelle Cumberbatch]

Can You help me!!
SW from commercial area are to be collected using a stationary-container system having 5 m3 containers. Determine an appropriate truck capacity for following conditions:

 

[IRstuff]

No free answers; please show your work to date

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[Isabelle Cumberbatch]

Please help me!

 

[IRstuff]

Please refrain from double posting, particularly since you are a student.
Show your work, or ask as specific question about the problem statement that you don't understand

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[fel3]

Isabelle...

Every problem, whether in school or at work, is easier to solve when broken down into small, easy to handle parts, and many problems are easier to understand after drawing a diagram or two. This problem is no different. I suspect you don't know where to start because this is a word problem with multiple steps that you need to develop, rather than just an equation to solve.

I suggest starting with this approach:
[ul]
[li]Separate the data into categories and pay attention to the units. For example, what does your second sentence, the first three bullets, and (later) some simple arithmetic tell you?[/li]
[li]Figure out if there is any unnecessary data. Some professors like to do this to trip up students. This is not a bad thing, actually. (BTW, both my EIT (1979) and PE (1983) exams included a couple problems with unnecessary data.)[/li]
[li]Figure out if there is any missing data that may require you to make reasonable assumptions. For example, is the speed limit the average speed for those legs of the day's travel? I doubt it, but then what would the estimated average speed be? If you make such an estimate, be sure to explain it in your calculations. (BTW, my PE exam was 8 problems in 8 hours, show your work. Every problem required me to make and justify at least one assumption, such as pipe roughness coefficient, concrete and rebar strengths, etc.)[/li]
[li]You know what the required answer is (truck capacity), but you can also help the solution process by figuring out what numbers you need that go into the final answer and maybe even the numbers that go into the step before. That is, sometimes you need to look at a problem both forwards and backwards to develop the steps in the algorithm that will produce the desired result. Also pay attention to what numbers must be integers, which might require a round-off at the appropriate time to produce an integer. Fortunately, this problem requires only simple arithmetic and simple algebra (i.e. no hyperbolic trig functions, complex numbers, or partial differentials).[/li]
[li]Draw a diagram of the day's events, path of travel, and times, and label each part with the data you know. Figure out when during day the truck goes to the disposal site (Hint, it's probably not first thing in the morning ). This diagram will have one or more unknowns when you first draw it, so make a representation of the unknown(s) for schematic purposes and note what the unknown(s) is/are. After you have solved the problem, I suggest redrawing the diagram with the unknowns resolved, then recheck your answer.[/li]
[/ul]

Word problems trip up most people, including many engineers. However, in the working world, most of our problems start as word problems. Many/most of these problems have insufficient or invalid* data and other "inconveniences." Our job as professionals is to take what we know, what we can reasonably assume, and apply our training and experience to come up with a solution that won't get us sued. :-(

*About 15 years ago I was the Engineer of Record for the site civil design for a new mental health building at an existing California state prison. One of our tasks was to evaluate the existing on-site utilities (water distribution, sewage collection, storm drainage collection, natural gas distribution, and electrical distribution) for capacity and (where possible) physical condition. The quality of the data (e.g. water and natural gas demands, pipe sizes, electrical demands, wire gauges, etc.) varied quite a bit and some data was simply missing. The best data was for the water system and the worst data was for the natural gas system. For natural gas, I was provided with five years worth of monthly meter readings and billing records from Pacific Gas & Electric Co. and daily meter readings made by site staff. The problem was that the daily readings totaled to more than three times the PG&E monthly readings and neither one was close to the predicted values based on the capacities of onsite gas-fired equipment and gas usage at other state prisons (the predicted values were about half-way between the two data sets). The daily readings followed the correct weekly pattern (lower usage on the weekends and holidays because the laundry was not used on those days), but the totals didn't make sense and neither did PG&E's totals. The site had commissioned a leakage test within the previous year, so leakage did not appear to the reason the daily readings were so high. I ran some flow/pressure calculations based on the three different sets of data (PG&E, predicted averages, and staff) and asked site staff to get me some pressure gauge readings so I could take a stab as resolving this difficulty, but I never got them. In the end, my evaluation boiled down: your data is funky, all your equipment seems to be operating just fine (i.e. no known pressure or flow problems), and some of your pipes are old Aldyl-A, which is prone to cracking and should be physically inspected ASAP by an expert in this type of pipe. Real engineering is often this "messy." But that's also part of what makes it fun.

Fred

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[waross]

Not enough information.

Determine an appropriate truck capacity for following conditions:

Truck capacity is generally expressed in Lbs or Tonnes.
There is no specific weight given for the waste nor any indication of the mass or volume to be transported each day.
No indication of loading time.
The problem is unsolvable as stated.
Is the truck transporting the containers or loading and compacting the waste. (probably)

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[fel3]

Waross...

Considering this is a school problem, there is sufficient information to solve it. Truck capacity will be in m^3. Not the best, I realize, but still valid. The OP's second sentence and the first three bullets give compacted volume per stop. I assume the unloading time is included in the other times (a simplification for the purposes of a school problem), etc. The only real unknown to me is whether the speed limit on the run to the disposal site equals the actual speed. In real life it won't, which is why I suggested an assumed lower speed for these runs. I solved the problem yesterday in about five minutes. It's not a difficult problem.

Fred

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[waross]

5 m3 containers

Container utilization factor: 0.7
Average number of containers at each location: 2
Collection vehicle compaction ratio: 2.5
Unloading time:
Drive time:
Distance:
Speed limit:
Time from garage:
Time from last container:
Number of trips to disposal site per day: 2
Length of working day: 8hr.
Raw volume of waste = 5 containers x 3m = 15 m^3
15 m^3 x .7 utilization = 10.5 m^3
10.5 m^3 / 2.5 compaction ratio = 4.2 m^3
4.2 m^3 / 2 trips per day = 2.1 m^3 truck capacity.
I doubt that garbage compactor truck are available that small.
If that was bailed at 1m x 1m x 2.1m it would easily fit in the box of an F150.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[fel3]

waross...

Please recheck your volume calculation. Each site averages two containers, each with a volume of 5 m^3, so 10 m^3 capacity per site, then apply the utilization and compaction factors.

Then, you still need to figure out how many sites can be serviced during an eight hour day. With two trips to the dump each day, the truck capacity is based on two four-hour half-shifts. Figuring out the number of sites is where all the time elements in the problem statement come into play.

Fred

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[IRstuff]

There's still missing parameters/assumptions, like:

> do you have to go back to the garage before you go to the dump?
> Is the dump the same distance to the first location as the last?
> how long does the truck stay at the dump, i.e., long does it take to dump its load?

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[fel3]

IRstuff

> do you have to go back to the garage before you go to the dump?
Since this is not mentioned, it is reasonable to assume no.
> Is the dump the same distance to the first location as the last?
Since only one one-way haul distance is specified, it is reasonable to assume the same distance.
> how long does the truck stay at the dump, i.e., long does it take to dump its load?
For my solution, I assumed time at the dump was equal to container unloading time. This is unrealistic, so is a legitimate unknown that I missed.

However, it is important to remember that this is a school problem and school problems are typically extreme simplifications of the real world. Their purpose is to teach principles, rather than attempt to solve a real-world problem.

Fred

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[IRstuff]

Sure, I got that, Fred, but these are things that certain TAs potentially downgrade, for not stating what the assumptions the OP might have used, and that might have been the intent of the problem, particularly since college is where one should start learning that problem statement often don't contain all the required information.

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[fel3]

IRstuff...

Agreed. That's why I initially suggested making an assumption regarding average speed to and from the dump that was some fraction of the posted speed limit. That being said, there is enough information and HINTS (which I should have added above) in the problem statement to create a solution.

Fred

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill