# Heat system efficiency?

1. Oct 14, 2004

### jin

heat system efficiency??

So lost..so what am i suppose to do??

'An engine absorbs 400J of heat and does 120J of work in each cycle'

a)what is its efficiency?
b)how much heat is rejected in each cycle?

2. Oct 14, 2004

### spacetime

For a cycle, that is, when after a process, a system comes back to its original state, the difference of the net energy taken and work done by it is zero - first law of thermodynamics.

$$Efficiency = \frac{work done}{energy taken}$$

spacetime
www.geocities.com/physics_all/index.html

3. Oct 14, 2004

### jin

so...i just go 120/400 x 100?

how do i calculate th heat rejected in the cycle?? the left over? 400-120??

4. Oct 15, 2004

### spacetime

correct!

spacetime

5. Oct 15, 2004

### jin

thanks! can u help me with the others on another post?? please ><