Firefighter Practice Exam

What is the displacement of a piston with a bore of 3.25 inches and a stroke of 4.75 inches?

1. 39.41 cubic inches

2. 47.59 cubic inches

3. 132.52 cubic inches

4. 157.62 cubic inches

The correct answer is: 39.41 cubic inches

To find the displacement of a piston, you can use the formula for the volume of a cylinder, which is: \[ \text{Volume} = \pi \times \left(\frac{\text{bore}}{2}\right)^2 \times \text{stroke} \] In this case, the bore (diameter) is 3.25 inches, and the stroke (length of the piston travel) is 4.75 inches. First, you need to calculate the radius by halving the bore: \[ \text{Radius} = \frac{3.25}{2} = 1.625 \text{ inches} \] Next, you square the radius: \[ \text{Radius}^2 = (1.625)^2 = 2.640625 \text{ square inches} \] Now, multiply by the stroke and by π (approximately 3.14159): \[ \text{Volume} = \pi \times 2.640625 \times 4.75 \] Calculating this gives: \[ \text{Volume} \approx 3.14159 \times 2.640625 \times 4.75 \approx 39.41 \