Question

Try the following experiment away from traffic where you can do it safely. With the car you are driving moving slowly on a straight, level road, shift the transmission into neutral and let the car coast. At the moment the car comes to a complete stop, step hard on the brake and notice what you feel. Now repeat the same experiment on a fairly gentle, uphill slope. Explain the difference in what a person riding in the car feels in the two cases. (Brian Popp suggested the idea for this question.)

Short answer

A person does not feel pushed inside a car when the brake is slammed at zero speed on a level road. But, a person is flung backwards against his seat if the brakes are slammed at zero speed on an upward incline.

Step-by-step solution

Define acceleration.

The rate of change of the velocity of an object with respect to time is known as acceleration.

Explain the two cases of riding in a car.

A person does not feel pushed inside a car when brakes are slammed at zero speed on a level road. As the car coasts to a stop, the forces of the rolling resistance and air resistance reduces to zero, so the car's acceleration is zero at that moment and even in the future. Whereas, a person is flung backwards against his if the brakes are slammed at zero speed on an upward incline. This is because, if the brakes are not stepped on, the car will accelerate downhill before, during, and after the zero speed instant.