If the fuel consumption of a car, travelling at a steady 60 mph is 20 mpg what is the power produced by the petrol being burnt in the engine ? (Assume that the density of petrol is 0.84 kg/l and the heat of combustion of petrol is 47 302 kJ/kg. I need the calculations. Thanks

To find power, you need to know the formula:



P is the power, E the energy and t the time.

Now, how much energy is your car using?
For each kilogram, it uses 47 302 kJ.

How many kilograms of fuel is it using?
Since each litre weighs 0.84 kg, you can find the total mass of fuel the car uses.

In brief, first find the number of gallons consumed (it consumes 1 gal for 20 miles, how many does it use for 60 miles?)
Find the equivalent amount of litres.
1 litre has a mass of 0.84 kg.
Find the total mass of fuel that of the amount of litres.
Then, find the energy that that amount gives out.
That energy is given out within one hour.
Find that in seconds.

Of course, I'm working using SI units, so, you have to convert all into the respective units, that is gallons to litres, and then litres to cubic metres. The distance won't matter, because they cancel out.

[Note that we are not allowed to do the homework, but only to give help in the form of guidance.]