# Energy conumption during accel, cruise and decel of a car

1. Sep 12, 2009

### tomislavp4

1. The problem statement, all variables and given/known data
A car with a mass of 1100 kg accelerates from 0 to 8,33 m/s in 15 s than cruises at 8,33 m/s in 20 s, it than decelerates to 0 in 15 s. It has 20% regenerative braking ability Cda of 0,4 and the coefficient of rolling resistance for the tires is 0,03. How much energy did it consume?

2. Relevant equations
Kinetic energy (J/s) = 0,5 * mass * 9,82 * velocity squared
Consumption during cruise = Air resistance + rolling resistance
Consumption during acceleration (J/s) = cruise consumption at starting speed + difference in kinetic energy / accelerating time
Rolling resistance = coefficient of rolling resistance * mass * 9,82
Air resistance = 0,5 * CdA *1,2 * velocity squared

3. The attempt at a solution
0 to 8,33 = 29484,63 J/s or 374769,45 J total
8,33 cruise = 340,71 J/s or 6814,27 J total
8,33 to 0 = -74953,89 J total

which gives 306629,83 J consumed. Do you guys see a problem somewhere?
It´s not a homework but it is connected with school so I´m sorry if it is in the wrong section, thanks!