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Question

A cylindrical rod has an outer curved surface area of \(7500 \text{ cm}^2\). If the length of the rod is 92 cm, then the outer radius (in cm) of the rod, rounded off to two places of decimal, is:
\(\left(\text{Take } \pi = \frac{22}{7}\right)\)

This question was previously asked in
RRB ALP 2025 CBT 2 Wiremen Question Paper (28-Jul-2026) (Shift 2)
The correct answer is
12.97

Cylindrical Rod Surface Area Calculation

The problem asks for the outer radius of a cylindrical rod given its outer curved surface area and length.

Given Information:

  • Outer Curved Surface Area = \(7500 \text{ cm}^2\)
  • Length (Height, \(h\)) = \(92 \text{ cm}\)
  • Value of \(\pi = \frac{22}{7}\)

Formula for Curved Surface Area of a Cylinder:

The formula for the curved surface area (CSA) of a cylinder is:

CSA = \(2 \pi r h\)

where \(r\) is the radius and \(h\) is the height (or length) of the cylinder.

Calculating the Radius:

  1. Substitute the given values into the formula:

    \(7500 = 2 \times \frac{22}{7} \times r \times 92\)

  2. Simplify the equation:

    \(7500 = \frac{44}{7} \times 92 \times r\)

    \(7500 = \frac{4048}{7} \times r\)

  3. Isolate the radius (\(r\)):

    \(r = \frac{7500 \times 7}{4048}\)

  4. Perform the calculation:

    \(r = \frac{52500}{4048}\)

    \(r \approx 12.969367... \text{ cm}\)

  5. Round the result to two decimal places:

    \(r \approx 12.97 \text{ cm}\)

The outer radius of the rod is approximately 12.97 cm.

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Similar Questions

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Important Questions from Mensuration 3D (Notes)

  1. The height of a cylinder is 14cm and its curved surface area is 264cm². The volume of the cyclinder (in cm³) is:
    ($\pi=\frac{22}{7}$)
  2. A number of 512 identical small spheres are cast from a sphere of radius 40 cm, with the total volume of the small spheres being equal to the volume of the larger sphere. The diameter (in cm) of each of the small spheres is:
  3. There is a wooden block in the form of a cube whose each side is 8 meters long. 

    The maximum possible number of cylinders with a diameter of 1 meter and a height of 4 meters were cut from this block. The cylinders are to be painted at the rate of ₹14 per square meter.
     

    What is the total amount (in ₹) needed to paint all the cylinders if we paint the entire surface of each cylinder? (Take $\pi = \frac{22}{7}$)

  4. If the lateral surface area of a cylinder is $140.1 \text{ cm}^2$ and its height is $3 \text{ cm}$, then find its volume. (Use $\pi = 3.14$ and round off to two decimal places.)
  5. Six cubes each of side 4 cm, are placed adjacent to each other. Find the volume of the cuboid so formed.
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