Section 1.16  Interactive checkpoint: cheeseburgers or gasoline?  
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A double cheeseburger contains 591 kilocalories of energy. A gallon of gasoline contains 159 MJ of energy. A compact car makes 39.0 miles/gallon on the highway. Assuming that it could run as efficiently on fast food as on gasoline, find the number of cheeseburgers needed to propel the car from New York to Chicago (719 miles).
 

A kilocalorie is a unit used to measure food energy, and is often called a Calorie, spelled with a capital C. One calorie (small c) is equal to 4.19 J (joules).

 

Answer:

N = cheeseburgers

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Diagram  [Hide]

Variables  [Hide]

Fill in the known values.

Variable

Value
energy in one cheeseburger

ECH = kcal

efficiency of car

e = mi/gal

energy in a gallon of gas

EG = MJ/gal

distance traveled

d = mi

gasoline needed

G

total energy needed

ET

number of cheeseburgers needed

N

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Strategy  [Hide]
  1. Determine the energy in each cheeseburger in joules.
  2. Determine the total energy needed in joules.
  3. Divide to get the number of cheeseburgers needed.
Physics principles and equations  [Hide]

1 mi = 1.61 km

1 cal = 4.19 J

Step-by-step solution   [Hide]
2

Select the conversion equation that will allow you to express the energy in a cheeseburger in joules.

Convert ECH to joules

ECH = ( kcal) × ( cal/kcal) × ( J/cal)

ECH = J

Find G

G = d / e

G = ( mi) / ( mi/gal)

G = gal

Find ET

ET = G × EG

ET = (18.4 gal) × ( MJ/gal) × ( J/MJ)

ET = J

Divide to find N

N = ET / ECH

N = (2.93×109 J) / (2.48×106 J/cheeseburger)

N = cheeseburgers
 
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