Hmm... Tricky Question

[brandon184]

I suck at all math stuff, so couldn't figure this out. I'm sure for some of you, it will take about 3 seconds.

The question is... You have a car that weighs 3000 pounds, has a 16.4 gallon gas tank, and gets (on average) 30 miles to the gallon. Now, if you were to add 230 pounds into the car's cargo - what would the decline in fuel economy be, and/OR how many gallons would you lose due to this extra 230 pounds in a 600 mile trip?

If any of you can figure it out, let me know... lol...

Oh yeah - This is for a friend who is embroiled in a battle, in which I'd like to assist in proving one side wrong.

Thanks.

~ Brandon

[brandon184]

^^

[krohnjw]

Heh, well I did some rudimentary calculations assuming constant speed and all the likes, and the MPG went from 30.00 to 27.94 ... I can send you the work if you want to see it, but it is just a quick work through.

You can make up the loss in fuel economy by applying duck tape to all the seams on the leading edge of your car. You know, smooth out the airflow...

[brandon184]

Thanks..!!

(It's $4 lost for every 600mi. I think.)

~ Brandon

[LinuxNewbie]

i got 27.86 miles per gallong but i did some funky math and i dont know why i did it.

30 miles per gallon per 3000 pounds = x miles per gallong per 3230 pounds and that looks like this:
30 / 3000 = x / 3230
but that indicates that as mas goes up, gas milage goes up and it gave me 32.xxxx miles per galon so i took 30 then divided by 32.xxxx and got a percentage which was 90 something percent then multiplied that percent by 30 and got this number.

i got fuzzy math

[Warthog]

lol...duct tape...

You might be a redneck if -

- You consider duct tape and tarp straps necessities
for auto body repair.
- The duct tape on your car seat sticks to your butt
when you get out.
- You refer to the duct tape on your car as "chrome".

[brandon184]

"- You refer to the duct tape on your car as "chrome"."

lol... I liked that one.

- the duck-tape gives your car's interior that "custom look"

[Theophylact]

It's not a math question, it's an engineering question, and one for experimentation, not theory. Look at it this way: suppose you could reduce the weight to 1000 pounds by throwing away everything but the engine, drive train and frame. Would the mileage then be 90 mpg? Naah. Chances are it might be 45 mpg, because most of the losses are in the power plant anyway. Smaller, lighter cars have smaller, lighter, less thirsty engines as well, and they don't get anywhere near 90 mpg.

Increasing the mass will cost you mileage, because it takes more energy to accelerate to a given speed: e=1/2 mv^2. But for non-ideal cases the situation isn't simple. Increasing the weight flattens your tires a bit more, causing more energy loss in tire flexing, for example. Your engine is most efficient at some specific rpm, probably about 3000 or so (just guessing); if you have to carry a load that requires you to use a lower gear for more power to overcome hills and air resistance, the revs will have to go up into a less fuel-efficient range, and so on. All these things have to be determined experimentally.