Answer: The total energy consumed by a car driving 100km is 3.22×108j;
(2)W = Fs = 644n× 100× 103m = 6.44× 107j；
Answer: the car is driving at a constant speed 100km, and the useful work done is 6.44 ×107j;
(3)η= W Q = 6.44× 107j 3.22× 108j = 20%；
The efficiency of this car is 20%;
(4) The total energy of gasoline combustion is converted into: ① useful energy for moving forward, ② extra work energy for overcoming mechanical friction, and ③ heat absorbed by the machine and evaporated into the air.