Final answer:
The efficiency of the heat engine is 21.43%. Therefore, the correct option is A) 21.43%.
Step-by-step explanation:
The efficiency of a heat engine is given by the ratio of the useful work output to the heat input. In this case, the heat engine exhausts 9800 J of heat while performing 2100 J of useful work. To find the efficiency, we divide the useful work by the heat input and multiply by 100 to express it as a percentage:
Efficiency = (Useful work / Heat input) x 100
Efficiency = (2100 J / 9800 J) x 100
Efficiency = 21.43%
Therefore, the efficiency of the heat engine is 21.43%.
Heat is a form of energy that transfers between objects due to a temperature difference. It flows from hotter objects to colder ones until thermal equilibrium (a state of balanced temperatures) is reached.