On complete combustion a litre of petrol gives off heat equivalent to

1.	On complete combustion a litre of petrol gives off heat equivalent to 3 × 107 J. in a test drive a car weighing 1200 kg, including the mass of driver, runs 15 km per litre while moving whit a uniform speed on a straight track. Assuming the friction offered by the road surface and air to be uniform, calculate the force of friction acting on the card during the test drive, if the efficiency of the car engine were 0.5.
Answer» ∴ Energy given by car in 1 litre petrol = 0.5 × 3 × 10⁷ J = 1.5 × 10⁷ Joule With 0.5 efficiency, 1 litre generates 1.5 × 10⁷ J. which is used for 15 km drive Fd = 1.5 × 10⁷ J, where d = 1.5 × 10⁴ m Force of friction F = \(\frac{1.5\times 10^7\,J}{1.5\times 10^4\, m}\) F = 10³ N

On complete combustion a litre of petrol gives off heat equivalent to 3 × 107 J. in a test drive a car weighing 1200 kg, including the mass of driver, runs 15 km per litre while moving whit a uniform speed on a straight track. Assuming the friction offered by the road surface and air to be uniform, calculate the force of friction acting on the card during the test drive, if the efficiency of the car engine were 0.5.

Answer»

∴ Energy given by car in 1 litre petrol

= 0.5 × 3 × 10⁷ J

= 1.5 × 10⁷ Joule

With 0.5 efficiency, 1 litre generates 1.5 × 10⁷ J. which is used for 15 km drive

Fd = 1.5 × 10⁷ J, where d = 1.5 × 10⁴ m

Force of friction F = \(\frac{1.5\times 10^7\,J}{1.5\times 10^4\, m}\)

F = 10³ N

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