A moving car contains a lot of energy as kinetic energy | energy of motion. If y

Question

A moving car contains a lot of energy as kinetic energy | energy of motion. If your car is not a hybrid,when you stop by stepping on the brake, your energy of motion is transformed by friction (in the brakes, against the road) into thermal energy. It cant be re-used. Estimate how many gallons of gasoline you could save each time you stopped your car from a speed of 100 km/hr if you could store that energy somehow and re-use it. Estimate what fraction of your gasoline you could save on a typical trip. [Hint: Look up on the web how much energy is typically provided by a gallon of gasoline. Cite your source and state why you think it is reliable.]
Be sure to clearly state your assumptions and how you came to the numbers you estimated,since grading on this problem will be mostly based on your reasoning, not on the number you get for your
answer.

Explanation / Answer

If "m" is the mass of my car and it is moving with the speed of 100 km/h i.e 500/18 m/s. and suppose the total moment of inertia of all the parts of the car which is rotating be "I".

Then:-

Total kinetic energy = mv2/2 + I2/2

If radius of the wheel is "r" then since the motion of the wheels are pure rolling friction will do no work i.e no energy will be lost by friction and v = r*.

2 = v2/r2

Total energy = v2/2[m + I/r2]

After applying brakes, everything will stop. Hence Kinetic energy will be lost to heat energy.

Suppose a gallon of gasoline produces "E" amount of energy, then

v2/(2E)*[m + 1/r2] gallon of gasoline can be saved. Here you can put v as 500/18 m/s.

Sorry I am not able to find the link you asked for.

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