## Physics: Principles with Applications (7th Edition)

The kinetic energy is proportional to the square of the speed, i.e., $KE = \frac{1}{2} mv^{2}$. Moving at 60 km/h, the car has 4 times the kinetic energy that it does moving at 30 km/h. In other words, it takes four times as much work to accelerate the car from 0 to 60 km/h as it takes to accelerate the car from 0 to 30 km/h. From that, we conclude that going from 30 to 60 takes three times the work as going from 0 to 30.