Is my driving efficient?

Classical Mechanics Level 3

The fuel efficiency of a car is represented by the distance in kilometers it can run with one liter of fuel (or miles per gallon in the United States). It is well known that the fuel efficiency varies substantially according to the driver's driving habits.

Cindy is driving her Camry at 36 km/h on a straight road, when she spots a traffic light turn red 75 meters ahead. She decelerates at a constant rate, and 6 seconds later she stops right at the traffic light. She waits 2 minutes for the light to turn green, and then accelerates at a steady rate of \(2\text{ m/s}^2\) until she reaches her previous speed of 36 km/h. Then she cruises at a steady speed for 2 kilometers. Approximately what is her overall fuel efficiency in kilometers per liter? Round your answer to the nearest integer.

Details and Assumptions

  • The fuel consumption rate when decelerating or staying still at the red light is 20 ml/min.
  • The fuel consumption rate when driving at a steady speed is 30 ml/min.
  • The fuel consumption rate when accelerating at \(2\text{ m/s}^2\) is 1.2 ml/s.
  • Ignore any air resistance.
  • The given measures do not exactly represent the actual performance of a Camry.

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