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Question

A cylinder of height 4 cm and base radius 3 cm is melted to form a sphere. The radius of sphere is:

This question was previously asked in
SSC GD 2018 Question Paper Hindi (09-Mar-2019) (Shift 1)
The correct answer is

3 cm

Cylinder Volume Calculation

The volume of a cylinder is given by the formula:

$ V_{cylinder} = \pi r^2 h $

Given:

  • Cylinder base radius ($r$) = 3 cm
  • Cylinder height ($h$) = 4 cm

Substituting the values:

$ V_{cylinder} = \pi \times (3 \text{ cm})^2 \times (4 \text{ cm}) $

$ V_{cylinder} = \pi \times 9 \text{ cm}^2 \times 4 \text{ cm} $

$ V_{cylinder} = 36\pi \text{ cm}^3 $

Sphere Volume Calculation

The volume of a sphere is given by the formula:

$ V_{sphere} = \frac{4}{3} \pi R^3 $

Where $R$ is the radius of the sphere.

Equating Volumes

When the cylinder is melted to form a sphere, the volume remains constant. Therefore:

$ V_{cylinder} = V_{sphere} $

$ 36\pi \text{ cm}^3 = \frac{4}{3} \pi R^3 $

Solving for Sphere Radius

To find the radius $R$ of the sphere, we solve the equation:

  1. Cancel $\pi$ from both sides:

    $ 36 = \frac{4}{3} R^3 $

  2. Isolate $R^3$:

    $ R^3 = 36 \times \frac{3}{4} $

    $ R^3 = 9 \times 3 $

    $ R^3 = 27 $

  3. Find the cube root:

    $ R = \sqrt[3]{27 \text{ cm}^3} $

    $ R = 3 \text{ cm} $

The radius of the sphere is 3 cm.

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Similar Questions

  1. What is the perpendicular distance (in cm) between the parallel sides of a trapezium whose area is 108 sqcm. and the lengths of the parallel sides are 9 cm and 36 cm?

  2. The length and breadth of a painting are 15 cm and 10 cm respectively. A 1 cm wide border is made around the painting. What is the area of the border?

  3. Find the total surface area of a cube whose volume is 64 cm3 ?.

  4. The area of an equilateral triangle is 16√3 sq cm. What is its perimeter?

  5. If the curved surface area of a sphere increased by 44%, then by what percentage would its volume increase?

  6. The total area of a circle and a square is equal to 2611 sq. cm. The diameter of the circle is 42 cm. What is the sum of the circumference of the circle and the perimeter of the square?(Take π = \(\frac{22}{7}\))


Important Questions from Mensuration

  1. Length of a rectangle is 3 cm more than width of rectangle and the difference between area of circle and area of rectangle is 84 cm2. Fiind the length of rectangle if radius of circle is 7 cm. (circle > rectangle)

  2. If the difference between the perimeter of a square field A and its side is 48 cm. Side of square field B is 4 cm less than the side of square field A. Then, find the area of square field B.

  3. What is the perpendicular distance (in cm) between the parallel sides of a trapezium whose area is 108 sqcm. and the lengths of the parallel sides are 9 cm and 36 cm?

  4. The length and breadth of a painting are 15 cm and 10 cm respectively. A 1 cm wide border is made around the painting. What is the area of the border?

  5. Find the total surface area of a cube whose volume is 64 cm3 ?.

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