Composite Cross-Section: Trapezium with Semi-Circular Cut-Out

Composite Cross-Section: Trapezium with Semi-Circular Cut-Out

Secondary 1

The diagram shows the uniform cross-section of a solid paper weight \(ABCDE\), which is in the shape of a trapezium with a semi-circular hole \(ABC\) cut out of it. It is given that \(AC\) is parallel to \(DE\), \(AC=7\) cm, \(CD=15\) cm, \(DE=21\) cm, \(AE=13\) cm, and the height of the trapezium is \(12\) cm.

  1. Find the area of \(ABCDE\).
  2. The length of the prism is \(30\) cm. Calculate its
    1. volume.
    2. surface area.
  3. The prism is melted down and recast into a cylinder of radius \(8\) cm. Find the height of the cylinder.

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Answer:(a) \(149\text{ cm}^2\) (3 s.f.) (b)(i) \(4460\text{ cm}^3\) (3 s.f.) (b)(ii) \(2100\text{ cm}^2\) (3 s.f.) (c) \(22.2\text{ cm}\) (3 s.f.)

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