Question

Petrol engine output of 20kw and uses 4.5kgvof fuel for each hour of running.The energy given out when 1kg of petrol is burnt 4.8x10^7J

Answer 1

Answer on Question #57812-Physics-Mechanics

Petrol engine output of 20kw and uses 4.5kgvof fuel for each hour of running. The energy given out when 1kg of petrol is burnt 4.8x10^7J

What is efficiency of petrol engine?

Solution

The power that producing when petrol burning is

$$W_{in} = \frac{4.5 \cdot 4.8 \cdot 10^{7}J}{1 \text{ hour}} = \frac{4.5 \cdot 4.8 \cdot 10^{7}J}{3600 \text{ s}} = 60 \text{ kW}.$$

The efficiency of petrol engine is

$$\eta = \frac{W_{out}}{W_{in}} = \frac{20 \text{ kW}}{60 \text{ kW}} = \frac{1}{3}.$$

Answer: $\frac{1}{3}$

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