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1.1. The diagram below shows a drinking glass with an inner diameter of 50mm and a height h. Ignore the thickness of the glass. The volume of the glass is 250 cm³. Calculate the height h. 1.2 Water is now poured into the glass until it is 65% full. Calculate the total surface area coved by the water

Mathematics

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2 parts
1.1

12.73 cm12.73 \text{ cm}

1.2

169.27 cm2169.27 \text{ cm}^2

Step-by-step solution

7 steps

Part 1.1· 3 steps

Calculate the height h.

  1. Convert the given diameter to radius in centimeters.

    The diameter is 50 mm50 \text{ mm}.
    The radius r=50 mm2=25 mmr = \frac{50 \text{ mm}}{2} = 25 \text{ mm}.
    Since 1 cm=10 mm1 \text{ cm} = 10 \text{ mm}, the radius in centimeters is r=2510 cm=2.5 cmr = \frac{25}{10} \text{ cm} = 2.5 \text{ cm}.
    The volume of the glass is given as V=250 cm3V = 250 \text{ cm}^3.

  2. Use the formula for the volume of a cylinder.

    The volume of a cylinder is given by V=πr2hV = \pi r^2 h.

  3. Substitute the known values and solve for hh.

    250 cm3=π(2.5 cm)2h250 \text{ cm}^3 = \pi (2.5 \text{ cm})^2 h 250=π(6.25)h250 = \pi (6.25) h h=2506.25πh = \frac{250}{6.25 \pi} h=40π cmh = \frac{40}{\pi} \text{ cm} h≈12.73 cmh \approx 12.73 \text{ cm}

    The height hh is approximately 12.73 cm\boxed{12.73 \text{ cm}}.

Part 1.2

169.27 cm2169.27 \text{ cm}^2

Calculate the total surface area covered by the water.

  1. Calculate the height of the water.

    The glass is 65%65\% full, so the height of the water (hwaterh_{water}) is 65%65\% of the total height hh.

    hwater=0.65×hh_{water} = 0.65 \times h hwater=0.65×40π cmh_{water} = 0.65 \times \frac{40}{\pi} \text{ cm} hwater=26π cmh_{water} = \frac{26}{\pi} \text{ cm} hwater≈8.28 cmh_{water} \approx 8.28 \text{ cm}
  2. Determine the components of the surface area covered by the water.

    The total surface area covered by the water includes:

    • The area of the bottom circular base of the glass: Abottom=πr2A_{bottom} = \pi r^2
    • The curved surface area of the glass in contact with the water: Acurved=2πrhwaterA_{curved} = 2 \pi r h_{water}
    • The area of the top surface of the water: Atop=πr2A_{top} = \pi r^2 The total surface area (AtotalA_{total}) is the sum of these three areas:
    Atotal=Abottom+Acurved+AtopA_{total} = A_{bottom} + A_{curved} + A_{top} Atotal=πr2+2πrhwater+πr2A_{total} = \pi r^2 + 2 \pi r h_{water} + \pi r^2 Atotal=2πr2+2πrhwaterA_{total} = 2 \pi r^2 + 2 \pi r h_{water}
  3. Substitute the values for rr and hwaterh_{water} into the formula.

    We have r=2.5 cmr = 2.5 \text{ cm} and hwater=26π cmh_{water} = \frac{26}{\pi} \text{ cm}.

    Atotal=2π(2.5 cm)2+2π(2.5 cm)(26π cm)A_{total} = 2 \pi (2.5 \text{ cm})^2 + 2 \pi (2.5 \text{ cm}) \left(\frac{26}{\pi} \text{ cm}\right) Atotal=2π(6.25 cm2)+2(2.5 cm)(26 cm)A_{total} = 2 \pi (6.25 \text{ cm}^2) + 2 (2.5 \text{ cm}) (26 \text{ cm}) Atotal=12.5π cm2+130 cm2A_{total} = 12.5 \pi \text{ cm}^2 + 130 \text{ cm}^2
  4. Calculate the total surface area.

    Atotal≈12.5×3.14159+130A_{total} \approx 12.5 \times 3.14159 + 130 Atotal≈39.269875+130A_{total} \approx 39.269875 + 130 Atotal≈169.27 cm2A_{total} \approx 169.27 \text{ cm}^2

    The total surface area covered by the water is approximately 169.27 cm2\boxed{169.27 \text{ cm}^2}.

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