Consider the following scenario. A car for which friction is not negligible acce

Question

Consider the following scenario. A car for which friction is not negligible accelerates from rest down a hill, running out of gasoline after a short distance. The driver lets the car coast farther down the hill, then up and over a small crest. He then coasts down that hill into a gas station, where he brakes to a stop and fills the tank with gasoline. Identify the forms of energy the car has, and how they are changed and transferred in this series of events. (SeeFigure 7.34.)Figure 7.34

A car experiencing non-negligible friction coasts down a hill, over a small crest, then downhill again, and comes to a stop at a gas station

Consider the following scenario. A car for which friction is not negligible accelerates from rest down a hill, running out of gasoline after a short distance. The driver lets the car coast farther down the hill, then up and over a small crest. He then coasts down that hill into a gas station, where he brakes to a stop and fills the tank with gasoline. Identify the forms of energy the car has, and how they are changed and transferred in this series of events. (SeeFigure 7.34.)Figure 7.34 A car experiencing non-negligible friction coasts down a hill, over a small crest, then downhill again, and comes to a stop at a gas station

Explanation / Answer

assuming the base of the hill to be at zero height,

the car had potential energy and zero kinetic energy at the top of the first hill.

while accelerating with the use of gasoline, the chemical eneergy of the gasaoline and the potential energy of the car are converted to kinetic energy.

after the gasoline is exhausted, while coming down, the potential energy is gradually transformed into kinetic energy, and at the bottom of the first hill, the car has kinetic energy and zero potential energy.

while goping up the second crest, the kinetic energy is gradually transformed into potential energy,and at the top of the small crest, car has both kinetic and potential energies.

while coming down the small crest, the potential energy is transformed into kinetic energy and by the time it comes down, it has all kinetic and zero potential energy.

while braking, friction, a non conservative force acts on the car and deccelerates it, and while deccelerating, the kinetic energy of the car is transformed into heat energy which dissipates into the environment.

after coming to rest, the car has zero kinetic and potential energies

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