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A container consists of a right cylindrical part and a hemispherical part at the top, as shown in the picture and diagram below - NSC Technical Mathematics - Question 8 - 2019 - Paper 1

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Question 8

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A container consists of a right cylindrical part and a hemispherical part at the top, as shown in the picture and diagram below. The radius of both shapes is $x$ cm ... show full transcript

Worked Solution & Example Answer:A container consists of a right cylindrical part and a hemispherical part at the top, as shown in the picture and diagram below - NSC Technical Mathematics - Question 8 - 2019 - Paper 1

Step 1

8.1 Write down, in terms of x, the height of the cylindrical part of the container.

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Answer

The height of the cylindrical part can be expressed as: h=(662x)extcmh = (66 - 2x) ext{ cm}

Step 2

8.2 Show that the formula for the total volume (in cm³) of the container is given by:

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Answer

The total volume VV consists of two parts: the volume of the cylindrical part and the volume of the hemispherical part.

  1. Volume of the Cylinder: Volume of the cylinder = extπx2h=extπx2(662x) ext{π}x^2h = ext{π}x^2(66 - 2x)

  2. Volume of the Hemisphere: Volume of the hemisphere = rac{1}{2} imes rac{4}{3} ext{π}x^3 = rac{2}{3} ext{π}x^3

  3. Total Volume: V = ext{π}x^2(66 - 2x) + rac{2}{3} ext{π}x^3 Expanding this: V = 66 ext{π}x^2 - 2 ext{π}x^3 + rac{2}{3} ext{π}x^3 After combining the terms: V = 66 ext{π}x^2 - rac{7}{3} ext{π}x^3

Step 3

8.3 Hence, calculate the value of x that will maximise the total volume of the container.

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Answer

To find the maximum volume, we need to differentiate the volume function:

V'(x) = rac{dV}{dx} = 66 ext{π}(2x) - rac{7}{3} ext{π}(3x^2)

Setting the derivative to zero to find critical points: 0=132extπx7extπx20 = 132 ext{π}x - 7 ext{π}x^2

Factoring out extπx ext{π}x gives: 0=extπx(1327x)0 = ext{π}x(132 - 7x)

Thus, we have two solutions:

  1. x=0x = 0 (not valid as it's a container)
  2. x = rac{132}{7} ext{ cm}

Step 4

8.4 Hence, determine the maximum total volume of the container.

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Answer

Substituting x = rac{132}{7} into the volume formula:

Vigg( rac{132}{7}igg) = 66 ext{π}igg( rac{132}{7}igg)^2 - rac{7}{3} ext{π}igg( rac{132}{7}igg)^3

Calculating each term: 66 ext{π}igg( rac{132}{7}igg)^2 = rac{66 ext{π} imes 17424}{49} = rac{1140240}{49}

For the second term: - rac{7}{3} ext{π}igg( rac{132}{7}igg)^3 = - rac{7 ext{π} imes 132^3}{3 imes 7^3}

After completing these calculations, we get the maximum volume. The maximum volume can be expressed as: Vextmaxext(approximately)=24,576.74extcm3extor7823.02extπcm3V_{ ext{max}} ext{ (approximately)} = 24,576.74 ext{ cm}^3 ext{ or } 7823.02 ext{π cm}^3

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