Math Problem Statement

jawapan dalam matematik

Sebuah silinder terbuka di bahagian atas dengan ketinggian dua kali jejari tapaknya, diisikan air sehingga tiga perempat penuh. Sebanyak 539 mL air diperlukan lagi untuk memenuhkan silinder tersebut. Hitung luas, dalam unit cm², permukaan silinder. (Guna π = 22/7)

Solution

The problem is written in Malay and translates to the following:

Question: An open cylinder at the top has a height twice the radius of its base. It is filled with water until three-quarters full. An additional 539 mL of water is needed to completely fill the cylinder. Calculate the surface area of the cylinder in square centimeters (cm²). (Use π=227\pi = \frac{22}{7}).


Steps to solve:

  1. Understand the Cylinder Geometry:

    • The cylinder has an open top, so the surface area will consist of the base area and the lateral surface area.
    • Let rr be the radius of the base, and the height of the cylinder is 2r2r (as given).
  2. Volume Calculation:

    • The total volume of the cylinder is Vtotal=πr2h=πr22r=2πr3V_{\text{total}} = \pi r^2 h = \pi r^2 \cdot 2r = 2\pi r^3.
    • Initially, the cylinder is filled to three-quarters, so Vfilled=34×2πr3=3πr32V_{\text{filled}} = \frac{3}{4} \times 2\pi r^3 = \frac{3\pi r^3}{2}.

    When an additional 539 mL of water is added, the cylinder is completely full. Hence, the difference in volume is 539 mL, which is equivalent to 539 cm³.

    Therefore, the equation is: VtotalVfilled=539V_{\text{total}} - V_{\text{filled}} = 539 Substituting the volumes: 2πr33πr32=5392\pi r^3 - \frac{3\pi r^3}{2} = 539 Simplify the left-hand side: πr32=539\frac{\pi r^3}{2} = 539 Substituting π=227\pi = \frac{22}{7}: 227r32=539\frac{\frac{22}{7} r^3}{2} = 539 Simplify further: 11r37=539\frac{11 r^3}{7} = 539 Multiply both sides by 7: 11r3=539×7=377311 r^3 = 539 \times 7 = 3773 Divide by 11: r3=377311=343r^3 = \frac{3773}{11} = 343 Taking the cube root of both sides: r=3433=7cmr = \sqrt[3]{343} = 7 \, \text{cm}

  3. Calculate Surface Area:

    • The surface area of the open cylinder is the sum of the lateral area and the base area.
    • Lateral surface area Alateral=2πrh=2πr2r=4πr2A_{\text{lateral}} = 2\pi r h = 2\pi r \cdot 2r = 4\pi r^2.
    • Base area Abase=πr2A_{\text{base}} = \pi r^2.
    • Total surface area Atotal=Alateral+Abase=4πr2+πr2=5πr2A_{\text{total}} = A_{\text{lateral}} + A_{\text{base}} = 4\pi r^2 + \pi r^2 = 5\pi r^2.

    Substituting r=7r = 7 cm and π=227\pi = \frac{22}{7}: Atotal=5×227×72=5×227×49A_{\text{total}} = 5 \times \frac{22}{7} \times 7^2 = 5 \times \frac{22}{7} \times 49 Simplify: Atotal=5×22×7=770cm2A_{\text{total}} = 5 \times 22 \times 7 = 770 \, \text{cm}^2

Thus, the surface area of the cylinder is 770 cm².


Would you like a detailed explanation of any step or have additional questions?

Related Questions:

  1. How do you calculate the lateral surface area of a closed cylinder?
  2. What is the formula for the volume of a cylinder?
  3. How does changing the height of a cylinder affect its surface area?
  4. How can you derive the formula for the surface area of an open cylinder?
  5. If the radius is doubled, how will the surface area change?

Tip: Always double-check unit conversions (e.g., milliliters to cubic centimeters) when working with volumes.

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Math Problem Analysis

Mathematical Concepts

Geometry
Cylindrical Volume
Surface Area

Formulas

V = πr²h
Surface Area of Cylinder = 2πrh + πr²
π ≈ 22/7

Theorems

Volume of Cylinder Theorem
Surface Area of Cylinder Formula

Suitable Grade Level

Grades 8-10