An arc of a circle of radius 21 cm subtends an angle of 60∘ at the centre. Find : (i) the length of the arc. (ii) the area of the minor segment of the circle made by the corresponding chord.
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Answer: (i) 22 cm (ii) (231−44413)cm2≈40.05cm2
(i) Arc length =36060×2×722×21=22 cm.
(ii) Area of sector =36060×722×212=231cm2.
The triangle formed by the two radii and the chord is equilateral (angle 60∘, two equal sides), so its area =43×212=44413cm2.
Area of minor segment =231−44413≈231−190.95=40.05cm2.
In the given figure, diameters AC and BD of the circle intersect at O. If ∠AOB=60∘ and OA = 10 cm, then : (i) find the length of the chord AB. (ii) find the area of shaded region. (Take π=3.14 and 3=1.73)
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Answer: (i) AB = 10 cm (ii) 113.75 cm2
(i) OA = OB = 10 cm and ∠AOB=60∘, so △AOB is equilateral and AB = 10 cm.
(ii) The shaded region is the minor segment APB together with sector BOC.
∠BOC=180∘−60∘=120∘. Area of sector BOC =360120×3.14×100=104.67cm2 (approx).
Area of segment APB = sector AOB −△AOB=36060×3.14×100−41.73×100=52.33−43.25=9.08cm2 (approx).
Shaded area =3314+6314−43.25=157−43.25=113.75cm2.
In the given figure, AB is a chord of a circle of radius 7 cm and centred at O. Find the area of the shaded region if ∠AOB=90∘. Also, find length of minor arc AB.
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Answer: Area of shaded region = 14 cm2; minor arc AB = 11 cm
AB and CD are arcs of two concentric circles of radii 3.5 cm and 10.5 cm respectively and centred at O. Find the area of the shaded region if ∠AOB=60∘. Also, find the length of arc CD.
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Answer: Area of shaded region =3154≈51.33 cm2; arc CD = 11 cm
Shaded area = sector OCD − sector OAB =36060×722×(10.52−3.52).
A chord of a circle of radius 14 cm subtends an angle of 60∘ at the centre. Find the area of the corresponding minor segment of the circle. Also find the area of the major segment of the circle.
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Answer: Minor segment =(3308−493) cm2 ≈ 17.89 cm2; major segment =(31540+493) cm2 ≈ 598.11 cm2
Area of sector =36060×722×14×14=3308 cm2 ≈ 102.67 cm2.
The triangle formed is equilateral (two radii with 60∘ between them): area =43×142=493 cm2 ≈ 84.87 cm2.
Minor segment =3308−493 ≈ 17.89 cm2.
Area of circle =722×142=616 cm2.
Major segment =616−(3308−493)=31540+493 ≈ 598.11 cm2.
A horse is tied to a peg at one corner of a square shaped grass field of side 15 m by means of a 5 m long rope. Find the area of that part of the field in which the horse can graze. Also, find the increase in grazing area if length of rope is increased to 10 m. (Use π=3.14)
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Answer: 19.625 m2; increase = 58.875 m2
The horse grazes a quadrant (angle 90∘) of radius equal to the rope.