# Homework Help: Heat in an Engine

1. Jul 30, 2006

### KingTutATL

The hot reservoir for a Carnot engine has a temperature of 890K, while the cold reservoir has a temperature of 670K. The heat input for this engine is 4800J. The 670K reservoir also serves as the hot reservoir for a second Carnot engine. This second engine uses the rejected heat of the first engine as input and extracts additional work from it. The rejected heat of the first engine as input and extrats additional work from it. The rejected heat from the second engine goes into a reservoir that has a temperature of 420K. Find the total work delivered by the 2 engines?

I'm lost

2. Jul 30, 2006

### Andrew Mason

What is the efficiency of a Carnot engine? Remember:

$$\eta = \frac{W_{output}}{Q_H}$$

AM

3. Aug 1, 2006

### Mute

Also useful will be the fact that the efficiency is also

$$\eta = 1 - \frac{T_C}{T_H}$$

So, calculate the work output from the first engine, from that calculate the heat transfered to the first cold resevior... Wash, rinse, repeat to find the work output of the second engine, and you're pretty much in the clear.