All Exams Test series for 1 year @ ₹349 only
Question

A solid metallic cylindrical rod of radius 1.4 cm and length 24 cm is melted and recast as identical spherical balls of radius 2 mm. How many maximum such balls could be made?

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
4410

Cylinder Volume Calculation

The volume of a cylinder is given by the formula $ V_{cylinder} = \pi r^2 h $, where $ r $ is the radius and $ h $ is the height (or length).

  • Given cylinder radius $ r_{cyl} = 1.4 $ cm.
  • Given cylinder length $ h_{cyl} = 24 $ cm.
  • Calculate cylinder volume: $ V_{cyl} = \pi \times (1.4 \text{ cm})^2 \times (24 \text{ cm}) $ $ V_{cyl} = \pi \times 1.96 \text{ cm}^2 \times 24 \text{ cm} $ $ V_{cyl} = 47.04 \pi \text{ cm}^3 $

Spherical Ball 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.

  • Given spherical ball radius $ r_{sphere} = 2 $ mm.
  • Convert radius to cm: $ r_{sphere} = 2 \text{ mm} = 0.2 \text{ cm} $.
  • Calculate the volume of one spherical ball: $ V_{sphere} = \frac{4}{3} \pi \times (0.2 \text{ cm})^3 $ $ V_{sphere} = \frac{4}{3} \pi \times 0.008 \text{ cm}^3 $ $ V_{sphere} = \frac{0.032}{3} \pi \text{ cm}^3 $

Maximum Balls Calculation

To find the maximum number of balls, divide the total volume of the cylinder by the volume of a single spherical ball.

  • Number of balls $ N = \frac{V_{cyl}}{V_{sphere}} $
  • Substitute the calculated volumes: $ N = \frac{47.04 \pi \text{ cm}^3}{\frac{0.032}{3} \pi \text{ cm}^3} $
  • Simplify the expression: $ N = \frac{47.04}{\frac{0.032}{3}} $ $ N = 47.04 \times \frac{3}{0.032} $ $ N = \frac{141.12}{0.032} $ $ N = 4410 $

Therefore, 4410 maximum spherical balls could be made.

Was this answer helpful?

Similar Questions

  1. The radius of a 80 cm wide road roller is 77 cm. Find the number of revolutions that the roller will take to cover an area of $96.8 \text{ m}^2$. [Take $\pi = \frac{22}{7}$]
  2. The number of balls of radius 2 cm that can be made from a solid sphere of radius 4 cm is:

Important Questions from Solid Figures

  1. A cylindrical tube, open at both ends, is made of a metal sheet which is 0.5 cm thick. Its outer radius is 4 cm and length is 2 m. How much metal (in cm 3) has been used in making the tube?

  2. The volume of a right circular cone is 308 cm 3 and the radius of its base is 7 cm. What is the curved surface area (in cm 2) of the cone? (Take π =  \(\frac{22}{7} \) )

  3. The slant height and radius of a right circular cone are in the ratio 29 ∶ 20. If its volume is 4838.4 π cm 3, then its radius is: 

  4. Six cubes, each of edge 2 cm, are joined end to end. What is the total surface area of the resulting cuboid in cm 2?

  5. A solid cube of side 8 cm is dropped into a rectangular container of length 16 cm, breadth 8 cm and height 15 cm which is partly filled with water. If the cube is completely submerged, then the rise of water level (in cm) is:

Need Expert Advice?
Upcoming Exams
RRB ALP
July 28, 2026
RRB Group D
August 03, 2026
Test Series
RRB NTPC img
Railways
RRB NTPC Under Graduate 2026 New Mock Test Series
1459 Tests 2 Tests Free
213 Attempts
4.3(512)
English, Hindi, Telugu +7 More

Start Your Preparation with Prepp Mobile App

Download the app from Google Play & App Store
Download the app from Google Play & App Store
Prepp Mobile App