Energy needed for car to travel-thermodynamics

[aal0315]

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?

 

[gadje]

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?

 

[aal0315]

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.

 

[aal0315]

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 ?

 

[Unit Maestro]

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.