Final answer:
The average braking force required to stop a car with 620kJ of kinetic energy over 91m is 6800 N, which is found by dividing the kinetic energy by the stopping distance according to the work-energy theorem. Option C is correct.
Step-by-step explanation:
To find the average braking force acting on a car, one can use the work-energy theorem which states that the work done by the force is equal to the change in kinetic energy. Since the car comes to a stop, all of the car's kinetic energy will be dissipated by the force of braking.
In this scenario, a car has 620kJ of kinetic energy, and it stops in a distance of 91m. Using the formula for work (Work = Force × Distance) and setting it equal to the car's kinetic energy, we can calculate the force.
The work done by the brakes is 620,000 joules (since 1 kJ = 1,000 J), and the distance is 91 meters. Therefore, average braking force = Work / Distance = 620,000 J / 91 m, which gives us approximately 6800 N. So the correct answer is C, 6800 N.