Question 144 of 480
A bucket is 12 cm in diameter at the top, 8 cm in diameter at the bottom and 4 cm deep. Calculate its volume.
- A. 304π/3 cm3
- B. 144π cm3
- C. 128π cm3
- D. 72π cm3
Correct Answer:
A
Explanation
To find the volume of the bucket, we can model it as a frustum of a cone. A frustum is the portion of a cone that lies between two parallel planes cutting it. In this case, the top diameter is 12 cm, the bottom diameter is 8 cm, and the height (depth) is 4 cm.
### Step-by-Step Explanation
1. **Identify the Dimensions**:
- Top diameter (D1) = 12 cm, so the radius (R1) = D1/2 = 12/2 = 6 cm.
- Bottom diameter (D2) = 8 cm, so the radius (R2) = D2/2 = 8/2 = 4 cm.
- Height (h) = 4 cm.
2. **Volume Formula for a Frustum**:
The volume \( V \) of a frustum of a cone can be calculated using the formula:
\[
V = \frac{1}{3} \pi h (R_1^2 + R_1 R_2 + R_2^2)
\]
where:
- \( R_1 \) is the radius of the top base,
- \( R_2 \) is the radius of the bottom base,
- \( h \) is the height of the frustum.
3. **Substituting the Values**:
Now, we substitute the values we found into the formula:
- \( R_1 = 6 \) cm,
- \( R_2 = 4 \) cm,
- \( h = 4 \) cm.
Plugging these into the formula:
\[
V = \frac{1}{3} \pi (4) (6^2 + 6 \cdot 4 + 4^2)
\]
4. **Calculating the Terms**:
- Calculate \( 6^2 = 36 \).
- Calculate \( 6 \cdot 4 = 24 \).
- Calculate \( 4^2 = 16 \).
- Now, add these values together:
\[
36 + 24 + 16 = 76
\]
5. **Final Calculation**:
Now substitute back into the volume formula:
\[
V = \frac{1}{3} \pi (4) (76)
\]
\[
V = \frac{1}{3} \pi (304)
\]
\[
V = \frac{304\pi}{3} \text{ cm}^3
\]
### Conclusion
The correct answer is **A. \( \frac{304\pi}{3} \text{ cm}^3 \)**.
### Explanation of Other Options
- **Option B: \( 144\pi \text{ cm}^3 \)**: This value does not account for the correct dimensions of the frustum and is likely derived from incorrect calculations or assumptions about the shape.
- **Option C: \( 128\pi \text{ cm}^3 \)**: Similar to option B, this value does not match the calculated volume and suggests a misunderstanding of the frustum volume formula.
- **Option D: \( 72\pi \text{ cm}^3 \)**: This is significantly lower than the calculated volume and does not reflect the dimensions provided.
### Revision Summary
- The volume of a frustum of a cone is calculated using the formula \( V = \frac{1}{3} \pi h (R_1^2 + R_1 R_2 + R_2^2) \).
- Ensure to convert diameters to radii before substituting into the formula.
- Carefully perform arithmetic operations to avoid errors in calculations.
- The final volume for the given bucket dimensions is \( \frac{304\pi}{3} \text{ cm}^3 \).