Math Problem Statement

The diagram shows a solid metal cylinder with a base radius of 3x cm and height h cm. The metal cylinder is melted, and all the metal is used to make 270 spheres, each with a radius of (1/2)x cm. Find an expression, in its simplest form, for h in terms of x.

Solution

To solve the problem, let's break it into parts:

Step 1: Volume of the cylinder

The volume VV of a cylinder is given by: V=πr2hV = \pi r^2 h Here, the base radius rr is 3x3x cm and the height is hh cm. Substituting r=3xr = 3x, we get: Vcylinder=π(3x)2h=9πx2hV_{\text{cylinder}} = \pi (3x)^2 h = 9\pi x^2 h


Step 2: Volume of one sphere

The volume of a sphere is given by: V=43πr3V = \frac{4}{3} \pi r^3 The radius rr of each sphere is given as 12x\frac{1}{2}x. Substituting r=12xr = \frac{1}{2}x, we calculate the volume: Vsphere=43π(12x)3V_{\text{sphere}} = \frac{4}{3} \pi \left(\frac{1}{2}x\right)^3 Simplify (12x)3\left(\frac{1}{2}x\right)^3: Vsphere=43πx38=4πx324=πx36V_{\text{sphere}} = \frac{4}{3} \pi \cdot \frac{x^3}{8} = \frac{4\pi x^3}{24} = \frac{\pi x^3}{6}


Step 3: Total volume of 270 spheres

Since 270 spheres are made, the total volume of all the spheres is: Vtotal spheres=270Vsphere=270πx36V_{\text{total spheres}} = 270 \cdot V_{\text{sphere}} = 270 \cdot \frac{\pi x^3}{6} Simplify: Vtotal spheres=45πx3V_{\text{total spheres}} = 45 \pi x^3


Step 4: Equating the volumes

The metal cylinder is melted to make the spheres, so the total volume of the cylinder equals the total volume of the spheres: Vcylinder=Vtotal spheresV_{\text{cylinder}} = V_{\text{total spheres}} Substitute the expressions: 9πx2h=45πx39\pi x^2 h = 45 \pi x^3


Step 5: Solve for hh

Cancel π\pi on both sides: 9x2h=45x39x^2 h = 45x^3 Divide through by 9x29x^2 (assuming x0x \neq 0): h=45x39x2=5xh = \frac{45x^3}{9x^2} = 5x


Final Answer:

h=5xh = 5x

Let me know if you'd like a deeper explanation or have further questions!


5 Related Questions:

  1. How do you derive the formula for the volume of a cylinder?
  2. What is the significance of equating the volumes in this type of problem?
  3. How would the solution change if the number of spheres were different?
  4. What happens if the radius of the spheres is increased while keeping the cylinder dimensions constant?
  5. How can this concept be applied in real-life scenarios like recycling or manufacturing?

Tip:

Always double-check the units and dimensions when solving volume-related problems to ensure consistency and accuracy!

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Math Problem Analysis

Mathematical Concepts

Volume of a cylinder
Volume of a sphere
Equating volumes
Simplifying algebraic expressions

Formulas

Volume of a cylinder: V = πr²h
Volume of a sphere: V = (4/3)πr³

Theorems

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Suitable Grade Level

Grades 9-11