A rectangular strip 5cm x 25cm is rotated completely about the 25cm side. Find the volume and the total surface area of the solid generated.
Explanation
To solve for the volume and the total surface area of the solid generated by rotating the rectangular strip around its 25 cm side, follow these steps:
1. Volume Calculation
When a rectangle is rotated about one of its sides, it forms a cylinder.
- Height of the Cylinder (h): 25 cm
- Radius of the Cylinder (r): 5 cm (the other side of the rectangle)
Volume of the Cylinder:
\[
\text{Volume} = \pi r^2 h
\]
\[
\text{Volume} = \pi \times (5)^2 \times 25
\]
\[
\text{Volume} = \pi \times 25 \times 25
\]
\[
\text{Volume} = 625 \pi
\]
\[
\text{Volume} \approx 625 \times 3.14 = 1962.5 \text{ cm}^3
\]
2. Total Surface Area Calculation
The total surface area of the cylinder consists of:
- The lateral surface area
- The area of the two circular bases
Lateral Surface Area:
\[
\text{Lateral Surface Area} = 2 \pi r h
\]
\[
\text{Lateral Surface Area} = 2 \pi \times 5 \times 25
\]
\[
\text{Lateral Surface Area} = 250 \pi
\]
\[
\text{Lateral Surface Area} \approx 250 \times 3.14 = 785 \text{ cm}^2
\]
Area of the Two Circular Bases:
\[
\text{Area of one base} = \pi r^2
\]
\[
\text{Area of one base} = \pi \times 25
\]
\[
\text{Area of one base} = 25 \pi
\]
\[
\text{Total area of two bases} = 2 \times 25 \pi = 50 \pi
\]
\[
\text{Total area of two bases} \approx 50 \times 3.14 = 157 \text{ cm}^2
\]
Total Surface Area:
\[
\text{Total Surface Area} = \text{Lateral Surface Area} + \text{Area of the two bases}
\]
\[
\text{Total Surface Area} = 785 + 157 = 942 \text{ cm}^2
\]
So, the correct option is:
A. 942.86 cm²