A motorist driving at 25 meters/second decelerates to. 15 meters/second. The combined mass of the vehicle and the driver is 1.5 * 10³ kilograms. What is the amount of mechanical work done by the vehicle?.

Kinetic energy = (1/2) · (mass) · (speed) ²

= (500 kg) · (speed) ².

At 25 m/s, KE = (500 kg) · (25 m/s) ² = 312,500 joules

At 15 m/s, KE = (500 kg) · (15 m/s) ² = 112,500 joules

The transmission and the brakes had to soak up and get rid of

(312,500 - 112,500) = 200,000 joules.

That's a lot of energy.

You paid good money to buy the gas that supplied the energy.

Sadly, when you mashed the brakes, and the brakes turned

all that kinetic energy into heat, and all that heat blew away

in the wind, you didn't get any of your money back.