7. Compare the energy needed to move 20 people 10km with 5 cars of 4 people with 3 stops at a speed of 70km / h. 

With a bus that stops every 2000m and only reaches a speed of 45 km / h. 

Both engines have an efficiency of 30%, the car with 4 people weighs 1.4 tons, the bus 12.5 tons (including 20 people).

c_dA = 0.8m2 for the car and the bus is 3.2m high and 2.5m wide and has an air resistance coefficient of 0.5.