- #1

greypilgrim

- 538

- 36

## Homework Statement

The volume displacement in a car engine is 2000 cm

^{3}. During the power stroke, the mean pressure inside the cylinder is 15 bar.

- Compute the work performed by the engine in one revolution.
- Compute the engine's power assuming it runs at 3000 rpm.

## Homework Equations

$$W=-p\cdot \Delta V=-3000\text{ J}$$

$$P=\frac{3000\cdot\left|W\right|}{60 \text{ s}}=150\text{ kW}$$

## The Attempt at a Solution

Above numbers are the solutions given by the book. However I'm not sure if they are correct.

- Shouldn't the pressure exerted from the outside by the piston be relevant here, since this is what the gas is working against? Or do we need to assume an equilibrium between inside and outside pressure in a thermodynamic treatment? Is this justified in reality?
- Usual car engines are four-stroke, so there's a power stroke only in every second revolution. Shouldn't both numbers need to be divided by 2 because of this?