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Question

A cylindrical rod has an curved surface area of $4,900 \text{ cm}^2$. If the length of the rod is 97 cm, then the radius (in cm) of the rod, correct to two places of decimal, is:
Take $\pi = \frac{22}{7}$

The correct answer is

8.04

Cylindrical Rod Radius Calculation

The problem requires us to calculate the radius of a cylindrical rod using its given curved surface area and length. We need to apply the standard formula for the curved surface area of a cylinder and solve for the radius.

Given Information Analysis

Let's list the information provided:

  • Curved Surface Area ($A$) = $4,900 \text{ cm}^2$
  • Length of the rod (Height, $h$) = $97 \text{ cm}$
  • The value of $\pi$ to be used is $\frac{22}{7}$

Formula for Curved Surface Area

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

$$A = 2 \pi r h$$

Where:

  • $A$ represents the curved surface area
  • $\pi$ is the mathematical constant Pi
  • $r$ is the radius of the cylinder's base
  • $h$ is the height (or length) of the cylinder

Step-by-step Calculation

To find the radius ($r$), we need to rearrange the formula:

$$r = \frac{A}{2 \pi h}$$

Now, substitute the given values into the formula:

$$r = \frac{4900}{2 \times \frac{22}{7} \times 97}$$

First, calculate the value of $2 \pi h$:

$$2 \times \frac{22}{7} \times 97 = \frac{44}{7} \times 97$$

Multiply 44 by 97:

$$44 \times 97 = 4268$$

So, $2 \pi h = \frac{4268}{7}$.

Now, substitute this back into the equation for $r$:

$$r = \frac{4900}{\frac{4268}{7}}$$

To divide by a fraction, we multiply by its reciprocal:

$$r = 4900 \times \frac{7}{4268}$$

$$r = \frac{4900 \times 7}{4268}$$

$$r = \frac{34300}{4268}$$

Now, perform the division:

$$r \approx 8.03655...$$

Rounding to Two Decimal Places

The question asks for the radius correct to two decimal places. We look at the third decimal place, which is 6. Since 6 is 5 or greater, we round up the second decimal place.

$$r \approx 8.04 \text{ cm}$$

Therefore, the radius of the rod is approximately $8.04$ cm.

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Important Questions from 3-D Mensuration

  1. Find the total surface area of a closed cylinder having a base radius of 70 m and a height of 110 m. [Use π = \(22\over7\)]

  2. Which of the following is a geometrical figure with a three-dimensional geometry that has eight vertices and six rectangular faces?

  3. The curved surface area of a cylinder is half of its total surface area. If its height is 195 cm, then find its diameter (in cm).
  4. The diameter of the base and slant height of a right circular cone are 30 cm and 113 cm, respectively. Find the volume (in cm³) of the given cone.
    (Use $\pi = \frac{22}{7}$)

  5. The volume (in $m^3$) of a cube, each of whose edges is 42 m, is:
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