# Homework Help: Thermodynamics motorcycle

1. Feb 19, 2005

### Kelvin

In a motorcycle engine, after combustion occurs in the top of the cylinder, the piston is forced down as the mixture of gaseous products undergoes an adiabatic expansion. Find the average power involved in this expansion when the engine is running at 4000 rpm, assuming that the gauge pressure immediately after combustion is 15.0 atm, the initial volume is 50.0 cm$$^3$$, and the volume of the mixture at the bottom of the stroke is 250 cm$$^3$$. Assume that the gases are diatomic and that the time involved in the expansion is one-half that of the total cycle.

I know work done in adiabatic process is
$$W=\frac{p_2 V_2 - p_1 V_1}{\gamma - 1}$$

$$p_1 V_1^{\gamma} = p_2 V_2^{\gamma}$$

so $$V_1 = 50.0 \hbox{ cm^3}$$, $$p_1 = 15.0 \hbox{ atm}$$,
$$\gamma = \frac{7}{5}$$

but what is the final volume $$V_2$$, which I need to determine $$p_2$$?

2. Feb 19, 2005

### Staff: Mentor

Isn't the final volume given?

3. Feb 19, 2005

### Kelvin

actually, I don't even know what a motorcycle is, and how the cylinder looks like .......

what is meant by "the volume of the mixture at the bottom of the stroke" ?

4. Feb 19, 2005

### cronxeh

the volume of the mixture at the bottom of the stroke is the final Volume

This is a motorcycle

5. Feb 19, 2005

### Kelvin

I mean I don't know how "motorcycle engine" works, and how does the "cyclinder" looks like.....

6. Feb 19, 2005

### cronxeh

Last edited: Feb 19, 2005
7. Feb 19, 2005

### Kelvin

so the assumption that "the expansion is one-half that of the total cycle" is wrong? it should be 1/4 ?

8. Feb 19, 2005