a car uses an engine to move. 400 joules go to exhaust pipe. 100 joules are used to move the car . how many Joules does gasoline produce? what is efficiency of the engine?
Answers
Answer:
Kinetic energy = 0.5 * mass * velocity * velocity
KE of a 1 tonne car at 60mph:
60 mph ~= 27 metres / second
KE = 0.5 * 1000 * 27 * 27
= 360 kJ
That is *only* how much KE the car has at 60 mph. It ignores any changes in height, losses to heat in transmission, engine inefficiencies, wind resistance, and probably a lot of other things.
As work is done on an object, it gains or loses kinetic energy. Work is defined as the amount of force applied to an object multiplied by the distance travelled as the object accelerates.
Assume you're driving down a straight, empty highway. Over the course of a mile, you gradually accelerate at a constant rate (that is, the net force on your car remains constant). This takes 4 minutes because your average speed over this interval is 15 mph.Let's try it again, but this time you'll go from 0 to 60 mph in a mile. You only accelerate for 2 minutes because your average speed is 30 mph. In other words, you not only gain twice the speed, but you do so in half the time as in the first scenario. This means your car has four times the acceleration and, as a result, four times the net force. Four times the force applied over the same distance equals four times the work done and four times the kinetic energy gained by the car.
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