Energy needed for car to travel-thermodynamics

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Homework Help Overview

The discussion revolves around calculating the energy required for a car to travel a distance of 150 km, given the fuel efficiency in miles per gallon and the energy yield of gasoline. The problem involves thermodynamics and unit conversions related to fuel consumption.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the importance of unit conversion, particularly converting miles per gallon to kilometers per gallon and understanding the mass of gasoline based on its density relative to water. Questions arise about how to calculate the energy from the mass of gasoline and the energy yield.

Discussion Status

Participants are actively engaging with the problem, exploring various unit conversions and calculations. Some have provided partial calculations and insights into the process, while others express uncertainty about the next steps and the formulas needed to determine energy consumption.

Contextual Notes

There is an assumption that participants are familiar with the relationship between volume, mass, and density, as well as the energy yield of gasoline. The discussion also highlights the reliance on tools for unit conversion, indicating a potential gap in manual conversion skills among participants.

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Homework Statement


Gasoline yields 4.8x10^7 J/kg when burned. How much energy does a car use traveling a distance of 150 km if it gets 25 miles per (British) gallon? Assume that the density of gasoline is 68% that of water.


Homework Equations





The Attempt at a Solution


I don't really know where to begin with this question. All i know is that 25mpg is equal to 40.225km per gallon.
Any suggestions?
 
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The crux of this question really is in unit conversion. It assumes that you know that a litre of water has a mass of 1 kg so that you can work out the mass of 25 gallons of gasoline.

Does this help?
 
So i do 40.225 x 68% = 27.35 kg to get the mass of 25 gallons of gasoline?

and what next? I don't know a formula to figure out the energy given the information.
 
ok does this look right to anyone:
25gallons x 1.609 = 40.225km per gallon

150km/40.225 = 3.729 gallons to travel 150km

3.729 x 68% = 2.536kg

2.536 x 4.8x10^7J/kg = 1.22x10^9J ?
 
One of the most helpful tools I have found is the Unit Conversion in Excel (http://www.unitconversionaddin.com ). This simply works because students (like me) are able to do the unit conversion automatically in excel like a program. I don't have to either search on the internet for the conversion value or have to write out some excel function. The download is like 5 bucks and has saved me hours of stress and time.
 
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