# physics

### Answers

The work done by the braking force in bringing the car to a stop is equal to the change in the kinetic energy of the car, and is equal to the negative of the kinetic energy of the car at the start. The work done by the braking force is equal to -mxv^2, where m is the mass of the car (1660 kg) and v is the speed of the car (74 km/hr). The change in kinetic energy of the car is therefore equal to -1660 kg x (74 km/hr)^2, or -127400000 J. This means that in order to bring the car to a stop, the braking force had to do 127400000 J of work, and the carâ€™s kinetic energy changed from +127400000 J to 0 J.