# Heat problem

1. May 11, 2005

### jennypear

An engine with an output of 150W has an efficiency of 25%. It works at 10 cycles/s.

A. How much work is done in each cycle?
work=power(delta t) = 150 W * 1s = 150 J
work =15.0 J per cycle

**got part A correct

B. How much heat is given off in each cycle?
delta internal energy = delta work + delta heat
delta intergy = 0 bc its a complete cycle
delta heat = - delta work
delta heat = 15 J

**Part B isn't coming out.....please guide in the correct direction if possible.

2. May 11, 2005

### Staff: Mentor

Realize that what you are calling "delta heat" equals $Q_{in} - Q_{out}$. What you need to find is $Q_{out}$. Also recall the definition of efficiency: $\eta = W_{out}/Q_{in}$.