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Maximise a complete globe on a closed cylindrical base

A decorative monument for the 2010 Youth Olympic Games consists of a complete globe on a closed cylindrical base of radius rr and height hh. The globe radius is 1.25r1.25r. To minimise cost, the total surface area is fixed at 36.5 m236.5\text{ m}^2.

(i) Show that h=(146−33πr2)/(8πr)h=(146-33\pi r^2)/(8\pi r). marks

Hence find exactly:

(ii) the cylinder radius giving greatest total volume. marks

(iii) that maximum volume. marks

A sphere of radius RR has area 4πR24\pi R^2 and volume 4πR3/34\pi R^3/3.

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Complete globe above a closed cylindrical base. The globe radius is 1.25r, cylinder radius r and height h. The base has both circular ends; the diagram indicates the full sphere, not a hemisphere.
Complete globe above a closed cylindrical base. The globe radius is 1.25r, cylinder radius r and height h. The base has both circular ends; the diagram indicates the full sphere, not a hemisphere.
Complete globe above a closed cylindrical base. The globe radius is 1.25r, cylinder radius r and height h. The base has both circular ends; the diagram indicates the full sphere, not a hemisphere.

[2009/CJC/Promo/12]

CJC · Review problems · Question 11

A complete sphere and a closed cylinder contribute their full stated areas in this source model.

Read the worked solution