Effect of Automobile Speed

The table illustrates the effect of speed while driving a small car on the highway or interstate.  This is realistic data for a small car with mass 1050 kg (including driver).  Use physics concepts and calculations to fill in the table and explore the effect of speed on various outcomes when driving.  See footnotes for tips on doing the calculations.

	27 m/s (60 mph)	38 m/s (85 mph)
Kinetic Energy
Avg braking friction^1
Minimum stopping distance ^2
Total friction at speed^3	580 N	830 N
Power output of engine
Fuel Economy in km/gal^2,4
Gas used in one year^5
annual gasoline cost ($3/gal)
Energy wasted in one year ^4,5
CO2 released in one year^6
time it takes to go 16 km ^7

¹Assume a coefficient of friction of 0.90 and ignore the effect of air resistance (air resistance is very small in comparison to tire friction when braking).

²Use the work-energy theorem.

³These values are based on actual measurements and technical calculations and include three types of friction:  air resistance, rolling resistance, and internal engine friction.

⁴Assume constant speed, efficiency of 37%, and energy in one gallon of gasoline = 120 MJ.

⁵Assume a year of driving is 19000 km (12000 miles). 

⁶Burning one gallon of gasoline releases 9.0 kg of CO₂ into the atmosphere.

⁷Assume a constant speed and calculate the number of minutes to make the trip (a typical commute of 10 miles).  Presumably we drive faster to save time – is it worth it?