Question

If a gasoline engine has an efficiency of 21 percent and losses 780 J to the cooling system and exhaust during each cycle, how much work is done by the engine?

Answer 1

As we know that efficiency of engine is given as

$efficiency = \frac{W}{Q_i}$

also we know that

$Q_i - Q_o = W$

given that

$Q_o = 780 J$

efficiency = 21%

now we have

$0.21 = \frac{Q_i - Q_o}{Q_i}$

$0.21 Q_i = Q_i - 780$

$0.79Q_i = 780$

$Q_i =987.3J$

now we have

$W = 987.3 - 780 = 207.3 J$