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 1600kgcar 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

power of car = force * velcoity

Pc = 941* 6   = 5646 Watts

efficiency e = W/Q

KE of the car = 0.5 mv^2

KE = 0.5 * 1600 * 6*6

KE = 28800 J

Energy of gasoline = U = 1.4e8/1609 = 87010 J

so

efficiency = 28800/87010

e = 33.1 %

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