Physics question related to energy?

Question

A car is coasting down a hill, gaining energy as it goes. As they near a stop sign, the driver begins lightly pressing on the brakes. Where does the energy they gained from coasting down the hill go?

Thanks for the answer!

Answer 1

It goes into thermal energy (heat) as the brakes heat up due to friction and perhaps to other, less significant sources of energy loss (e.g. sound of brakes squealing).

Note: The car doesn't really gain energy, it just converts its gravitational potential energy (from being at the top of the hill) into kinetic energy (the energy associated with motion).

Answer 2

The pressure of the brake pads on the rotors increases the friction between the two. This friction creates heat, which is then radiated and convected into the atmosphere. So, coasting down hill leads to global warming.... Who is the they in your question? Is there more to this than meets the eye? Perhaps more than one occupant... And why were they surreptitiously coasting down a hill? Inquiring minds want to know.

As too gaining or loosing energy, it is a bit more complicated than Mr. Smartypants would indicate. You do gain potential energy by driving up the hill, at the expense of hydrocarbons. But, in the total energy budget of a car there is the rolling resistance (road/tire friction, efficiency of bearings) and the air resistance. Both of these are a function of velocity, and are no respecters of going up or down a hill. For instance, if you head out to a long hill and let your car roll, you will reach a maximum velocity for that slope. In my BMW, I hit ~100 kph on a 4% grade. Even this will change depending on air density. So, coasting down a hill "gaining energy" is only good for a certain velocity range.

Hope this helps!

Answer 3

Firstly, it's worth noting that the car isn't gaining energy as it goes down the hill, just converting it from one form to another. To begin with, it has potential energy due to its height at the top of the hill. As it rolls down the hill, this potential energy is converted to kinetic energy (associated with its increased velocity).

When the bakes are pressed, the car will slow down, and lose kinetic energy. This energy will therefore have to be converted into another form. In this case, most of it will be converted to heat energy as the brakes and wheels will heat up. If the brakes are noisy, some will also be converted to sound energy. hope this helps

Answer 4

Blue did good, but if it's an electric car, pressing on the brakes causes some of the kinetic energy to be converted to electrical energy and then to chemical energy which is stored in the propulsive battery.

Answer 5

The energy will be transferred to heat and sound via friction. I.e. the brakes will heat and make a squeak (if they are old!)

Answer 6

We need to bring Albert Enstein back to life to answer your question.