Math Problem Statement

  • The volume of a cylinder is directly proportional to its height and to the square of its radius. If the height is halved while the radius is tripled, what will be the percentage change in the volume of the cylinder?

Solution

The volume VV of a cylinder is given by the formula:

V=πr2hV = \pi r^2 h

where:

  • rr is the radius of the cylinder
  • hh is the height of the cylinder
  • π\pi is a constant (approximately 3.14159)

Now, we are given that the height is halved and the radius is tripled. Let's analyze the effect of these changes on the volume.

Original volume:

Voriginal=πr2hV_{\text{original}} = \pi r^2 h

New dimensions:

  • The new height is h2\frac{h}{2}.
  • The new radius is 3r3r.

New volume:

Vnew=π(3r)2(h2)V_{\text{new}} = \pi (3r)^2 \left( \frac{h}{2} \right) Simplifying the expression: Vnew=π(9r2)(h2)V_{\text{new}} = \pi (9r^2) \left( \frac{h}{2} \right) Vnew=92πr2hV_{\text{new}} = \frac{9}{2} \pi r^2 h

Change in volume:

To find the factor by which the volume changes, we compare the new volume to the original volume: VnewVoriginal=92πr2hπr2h=92\frac{V_{\text{new}}}{V_{\text{original}}} = \frac{\frac{9}{2} \pi r^2 h}{\pi r^2 h} = \frac{9}{2} So the volume becomes 92\frac{9}{2} or 4.5 times the original volume.

Percentage change:

The percentage change in volume is calculated as: Percentage change=(VnewVoriginalVoriginal)×100=(9211)×100=(4.51)×100=3.5×100=350%\text{Percentage change} = \left( \frac{V_{\text{new}} - V_{\text{original}}}{V_{\text{original}}} \right) \times 100 = \left( \frac{\frac{9}{2} - 1}{1} \right) \times 100 = \left( 4.5 - 1 \right) \times 100 = 3.5 \times 100 = 350\%

Thus, the volume of the cylinder increases by 350%.

Would you like more details or have any questions?

Here are 5 related questions to explore further:

  1. How does the volume of a cone compare to that of a cylinder with the same base and height?
  2. If both height and radius of a cylinder are doubled, how does the volume change?
  3. What is the relationship between surface area and volume in a cylinder?
  4. How would the volume of a cylinder change if the radius is doubled but the height remains constant?
  5. Can you find a real-life example where the cylinder volume formula is used?

Tip: When dimensions of a geometric shape change, calculating volume ratios can help identify the percentage change efficiently.

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Math Problem Analysis

Mathematical Concepts

Geometry
Volume of Cylinder
Proportions

Formulas

V = πr²h (Volume of a Cylinder)

Theorems

Direct Proportionality

Suitable Grade Level

Grades 8-10