## anonymous 5 years ago An engine burns 1.4 kg of gasoline per hour and yields 3.5 kW of power. Calculate the efficiency of the engine when the heating value of gasoline is 43 MJ/kg.

1. anonymous

i dont even know where to start

2. anonymous

ANY help, even a formula or a rule or a hint, anything will help

3. anonymous

i just know efficiency = input/output

4. anonymous

Yep, calm down.,,

5. anonymous

oh, sorry, it is output/input

6. anonymous

ok,.... i am calm

7. anonymous

The heating value is the amount of heat energy produced by complete combustion in a given quantity. Take a basis of 1 hour. Then your engine burns 1.4kg of gasoline, which yields a maximal amount of thermal energy to use for work as$43MJ/kg \times 1.4 kg=60.2MJ$In one hour, your engine produces from this energy, $\frac{3500J}{s}\times \frac{3600s}{h}=12.6MJ$The efficiency is the amount of work per unit energy input, which is $\eta = \frac{12.6MJ}{60.2MJ}=0.209$to 3 significant figures.

8. anonymous

This is the first time I've used 'heating value' for anything like this, so if the answer's wrong, I couldn't find an appropriate definition.

9. anonymous

so, can i say that efficiancy is 20.9%?

10. anonymous

Yes

11. anonymous

ok, thank you, i already faned you long time ago, so cant fan again :(

12. anonymous

Yeah I know - no worries :)

13. anonymous

The answer makes sense - I've seen values between 10 and 50% for internal combustion engines.

14. anonymous

then it is probably correct, i also know that cobustion engines are very unefficient

15. anonymous

hey anwar

16. anonymous

hi :)

17. anonymous

want a fan?

18. anonymous

would you be one if I say yes?

19. anonymous

...

20. anonymous

lol

21. anonymous

you got it

22. anonymous

thanks!!

23. anonymous

anwar, can you please fan lokisan, because he helped me alot and i can only fan him once

24. anonymous

25. anonymous

so you faned me just as an exchange for me to fan the guy huh? :(

26. anonymous

nah, would have faned you anyway

27. anonymous

lol andy, you and your fanning job~ ^_^