Posted by **jean** on Thursday, April 26, 2007 at 12:27am.

Heat engine X takes four times more energy by heat from the hot reservoir than heat engine Y. Engine X delivers two times more work, and it reject seven times more energy by heat to the cold reservoir than heat engine Y. Find the efficiency of heat engine X and heat engine Y.

Qin,x - Qout,x = Work,x

Qin,y - Qout,y = Work,y

Work,x = 2 Work,y

Qin,x = 4 Qin,y

Qout,x = 7 Qout,y

4Qin,y - 7Qout,y = 2 Work,y

7Qin,y - 7Qout,y = 7 Work,y

3Qin,y = 5Work,y

Since Efficiency = W/Qin,

Efficiency,y = 3/5

Work,x/Qin,x = 2Work,y/4Qin,y

Efficiency,x = (1/2)Efficiency,7 = 3/10

I got everything up until i got to the

7Qin,y - 7Qout,y= 7 Work,y

where did those numbers come from?

It is the same as the second equation on the list, with both sides multiplied by 7. It was one step in elimimating the Qout,y variable when combined with the equation above it.

## Answer this Question

## Related Questions

- Physics help please! - The engine has an efficiency e1. The engine takes input ...
- physics - A Carnot engine is operated between two heat reservoirs at ...
- physics - A Carnot engine is operated between two heat reservoirs at ...
- physics - The hot reservoir for a Carnot engine has a temperature of 926 K, ...
- Physics - Consider an inefficient engine which draws 200 J of heat from a hot ...
- Physics - Consider an inefficient engine which draws 200 J of heat from a hot ...
- Physics - Consider an inefficient engine which draws 200 J of heat from a hot ...
- Physics - Consider an inefficient engine which draws 200 J of heat from a hot ...
- Physics - Consider an inefficient engine which draws 200 J of heat from a hot ...
- Physic II - a carnot heat engine operates between reservoirs at 550K and 300K, ...