Driving on asphalt roads entails very little rolling resistance, so most of the

Question

Driving on asphalt roads entails very little rolling resistance, so most of the energy of the engine goes to overcoming air resistance. But driving slowly in dry sand is another story. If a 1300kg car is driven in sand at 6.0m/s , the coefficient of rolling friction is 0.06. In this case, nearly all of the energy that the car uses to move goes to overcoming rolling friction, so you can ignore air drag in this problem.

If the car gets 15 miles per gallon when driving on sand, what is the car's efficiency? One gallon of gasoline contains 1.4

Explanation / Answer

a) F = M*g*0.06= 1300*9.8*0.06 = 764.4 N

b) Power = F*V = 764.4* 6 = 4586.4N*m/s

c) For efficiency, you need the heating value of the fuel as well as the mpg.

Fuel required to go one mile = 1/15 gallon = 0.257 liters = 2.57*10^-4 m^3
Mass of fuel needed per mile = 0.185 kg
Multiply that by the heat value for the chemical energy input.

The delivered power out per mile is F*1609 meters = 1.14*10^6 J
chemical energy per gallon=1.4

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