The kinetic energy of a car is 7000 J as it travels along a horizontal road. How much work is required to stop the car in 20 s?

350 jouels is the correct answer

A car travels with a kinetic energy of 7000 J as it travels along a horizontal road how much work is required to stop the car?

The amount of work required, assuming that the brakes work at 100% efficiency is ... 7000 Joules.

 

The brakes transform the car's kinetic energy into heat energy. The rate (power) for this is 7000/20 Joules/second = 350 J/s

 

But wait! The proper unit for Joules/second is Watts. So the brakes dissipate the car's energy into heat as a rate of 350 Watts.