On complete combustion , a litre of petrol gives off heat equivalent to `3xx10^(7)J` . In a test drive, a car weighing 1200kg, including the mass of driver, runs 15kg per litre while moving with a uniform speed on a straight track. Assuming that friction offered by the road surface and air to be uniform, calculate the force of friction acting on the car during the test drive. If the efficiency of the car engine were `0.5.

Explanation

Here, 1 litre of petrol gives off `3xx10^(7)J` of energy.
As efficiency of engine is `0.5,` energy used by car `E=0.5xx3xx10^(7)J=1.5xx10^(7)J`
If F is force of friction , then `Fxxs=E`
`Fxx(15xx10^(3))=1.5xx10^(7)`
`F=10^(3)N`