On complete combustion,a litre of petrol rele | vedclass

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Question

(A) The energy input from the combustion of one litre of petrol is $E_{	ext{input}} = 3 	imes 10^7 \, J$.Given the efficiency of the engine $\eta =

Vedclass · Accepted Answer

$1000$

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(A) The energy input from the combustion of one litre of petrol is $E_{	ext{input}} = 3 	imes 10^7 \, J$.Given the efficiency of the engine $\eta = 0.5$,the useful work done by the engine is $E_{	ext{useful}} = \eta 	imes E_{	ext{input}} = 0.5 	imes 3 	imes 10^7 \, J = 1.5 	imes 10^7 \, J$.The car travels a distance $d = 15 \, km = 15 	imes 10^3 \, m$ using this energy.Since the car moves at a uniform speed,the work done by the engine is entirely used to overcome the force of friction $f$.Thus,$E_{	ext{useful}} = f 	imes d$.Substituting the values: $1.5 	imes 10^7 \, J = f 	imes 15 	imes 10^3 \, m$.Solving for $f$: $f = \frac{1.5 	imes 10^7}{15 	imes 10^3} = 0.1 	imes 10^4 \, N = 1000 \, N$.

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