Study MaterialsImportant QuestionsImportant Questions for Class 10 Maths Chapter 12 Areas Related to Circles

Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles

Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles

Areas Related to Circles Class 10 Important Questions Very Short Answer (1 Mark)

Question 1.
If the area of a circle is equal to sum of the areas of two circles of diameters 10 cm and 24 cm, calculate the diameter of the larger circle (in cm). (2012D)
Solution:
πR2 = πr21 + πr22
πR2 = π(r21 + πr22) [ r1 = \(\frac{10}{2}\) = 5cm, r2 = \(\frac{24}{2}\) = 12 cm] R2 = 52 + 122 = 25 + 144
R2 = 169 = 13 cm
∴ Diameter = 2(13) = 26 cm

Question 2.
The circumference of a circle is 22 cm. Calculate the area of its quadrant (in cm2). (2012OD)
Solution:
Circumference of a circle = 22 cm 2πr = 22 cm
Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 1

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    Question 3.
    If the difference between the circumference and the radius of a circle is 37 cm, then using π = \(\frac{22}{7}\), calculate the circumference (in cm) of the circle. (2013D)
    Solution:
    2πr – r = 37 ⇒ r(2π – 1) = 37
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 2

    Question 4.
    If he is taken as \(\frac{22}{7}\), calculate the distance (in metres) covered by a wheel of diameter 35 cm, in one revolution. (2013OD)
    Solution:
    Radius (r) = \(\frac{35}{2}\)
    Required distance = Perimeter = 2πr
    = 2 × \(\frac{22}{7}\) × \(\frac{35}{7}\) cm = 110 cm or 1.1 m

    Question 5.
    In Figure , find the area of the shaded region. (2011OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 3
    Solution:
    Area of shaded region
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 4

    Areas Related to Circles Class 10 Important Questions Short Answer-I (2 Marks)

    Question 6.
    The length of the minute hand of a clock is 14 cm. Find the area swept by the minute hand in 5 minutes. (2013OD)
    Solution:
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 5

    Question 7.
    PQRS is a diameter of a circle of radius 6 cm. The equal lengths PQ, QR and RS are drawn on PQ and QS as PToo RT diameters, as shown in Figure. Find the perimeter of the shaded region. (2011OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 9
    Solution:
    Radius OS = 6 cm
    ∴ Diameter PS = 12 cm
    ∵ PQ, QR and RS, three parts of the diameter are equal.
    ∴ PQ = QR = RS = 4 cm
    and QS = 2 × 4 = 8 cm
    ∴ Required perimeter
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 10

    Question 8.
    In Figure, a square OABC is inscribed in a quadrant OPBQ of a cirlce. If OA = 20 cm, find the area of the shaded region. (Use π = 3.14) (2014D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 11
    Solution:
    Diagonal of the square (OB) = Side \(\sqrt{2}\)
    ∴ r = 20\(\sqrt{2}\) cm …[Side of square, OA = 20 cm
    ∴ θ = 90°
    ar(Shaded region) = ar(Quad. Sector) – ar(Square)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 12

    Question 9.
    Two circular pieces of equal radii and maximum area, touching each other are cut out from a rectangular card board of dimensions 14 cm × 7 cm. Find the area of the remaining card board. [Use π = \(\frac{22}{7}\)] (2013D)
    Solution:
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 13
    Here r = \(\frac{7}{2}\) cm, L = 14 cm, B = 7 cm
    Area of the remaining card board
    = ar(rectangle) – 2(area of circle)
    = L x B – 2πr2)
    = 14 × 7 – 2 × \(\frac{22}{7}\) × \(\frac{7}{2}\) × \(\frac{7}{2}\)
    = 98 – 77 = 21 cm2

    Areas Related to Circles Class 10 Important Questions Short Answer-II (3 Marks)

    Question 10.
    Find the area of a quadrant of a circle, where the circumference of circle is 44 cm. (Use π = \(\frac{22}{7}\)] (2011OD)
    Solution:
    Circumference of a circle = 44 cm
    ⇒ 2πr = 44 cm
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 14

    Question 11.
    Area of a sector of a circle of radius 14 cm is 154 cm2. Find the length of the corresponding arc of the sector. [Use π = \(\frac{22}{7}\)] (2011OD)
    Solution:
    Area of sector = 154 cm2
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 15

    Question 12.
    In the Figure, PQ and AB are respectively the arcs of two concentric circles of a radii 7 cm and 3.5 cm and centre O. If ∠POQ = 30°, then find the area of the shaded region. [Use π = \(\frac{22}{7}\)] (2012D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 16
    Solution:
    Area of sector with radius 7 cm
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 17

    Question 13.
    In Figure, a circle is inscribed in an equilateral triangle ABC of side 12 cm. Find the radius of inscribed circle and the area of the shaded region. (Use π = 3.14 and \(\sqrt{3}\) = 1.73) (2014D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 18
    Solution:
    Area of an Equilateral ∆ = \(\frac{\sqrt{3}}{4}\) (side)2
    Construction: Draw OD ⊥ AB, OE ⊥ BC and OF ⊥ AC. Join OA, OB and OC.
    Proof: Area of ∆ABC
    = ar(∆AOB) + ar(∆BOC) + ar(∆AOC)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 19
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 20

    Question 14.
    In the figure, PSR, RTQ and PAQ are three semicircles of diameters 10 cm, 3 cm and 7 cm respectively. Find the perimeter of the shaded region. [Use π = 3.14] (2014D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 21
    Solution:
    Radius of circle QTR = r1 = \(\frac{3}{2}\) = 1.5 cm
    Radius of circle PAQ = r2 = \(\frac{7}{2}\) = 3.5 cm
    Radius of circle PSR = r3 = \(\frac{7+3}{2}\) = 5 cm
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 22
    Perimeter of the shaded region
    = πr1 + πr2 + πr3
    = π(r1 + r2 + r3)
    = 3.14(1.5 + 3.5 + 5)
    = 3.14(10) = 31.4 cm

    Question 15.
    In Figure, ABC is a triangle rightangled at B, with AB = 14 cm and BC = 24 cm. With the vertices A, B and C as centres, arcs are drawn, each of radius 7 cm. Find the area of the shaded region. (Use π = \(\frac{22}{7}\)) (2011OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 23
    Solution:
    Let ∠BAC = θ1, ∠ABC = θ2 and ∠ACB = θ3
    Area of the shaded region
    = ar(∆ABC) – [ar(sector A) + ar(sector B) + ar(sector C)] Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 24

    Question 16.
    Find the area of the major segment APB, in the figure of a circle of radius 35 cm and ∠AOB = 90°. (Use π = \(\frac{22}{7}\)) (2011D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 25
    Solution:
    Here θ = 90°, p = OA = OB = 35 cm
    Area of minor segment = ar(minor sector) – ar(∆AOB)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 26
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 27

    Question 17.
    A chord of a circle of radius 14 cm subtends an angle of 120° at the centre. Find the area of the corresponding minor segment of the circle. (Use π = \(\frac{22}{7}\) and \(\sqrt{3}\) = 1.73] (2011OD)
    Solution:
    Here θ = 120°, r = 14 cm
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 28

    Question 18.
    In Figure, a semi-circle is drawn with O as centre and AB as diameter. Semi-circles are drawn with AO and A OB as diameters. If AB = 28 m, find the perimeter of the shaded region. [Use π = \(\frac{22}{7}\) (2011OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 29
    Solution:
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 30

    Question 19.
    In a circle of radius 21 cm, an arc subtends an angle of 60° at the centre. Find:
    (i) the length of the arc
    (ii) area of the sector formed by the arc. [Use π = \(\frac{22}{7}\)] (2013D)
    Solution:
    (i) Length of the arc: r = 21 cm, θ = 60°
    Length of the arc
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 31

    Question 20.
    In Figure, two concentric circles with centre O, have radii 21 cm and 42 cm. If ∠AOB = 60°, find the area of the shaded region. (Use π = \(\frac{22}{7}\)] (2014OD, 2016OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 32
    Solution:
    1st Method: Here θ = 60°
    ∴ Area of the shaded region = ar (major sector of large circle) – ar (major sector of small circle)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 33

    2nd Method: Required area
    = ar (large circle) – ar (small circle) – ar (ABCD)
    = ar (large circle) – ar (small circle) – ar (minor sector of large circle) – ar (minor sector of small circle)

    3rd Method:
    Shaded region = ar (large circle)
    – ar (minor sector of large circle) – ar (major sector of small circle)

    Question 21.
    In Figure, APB and AQO are semi-circles, and AO = OB. If the peri-meter of al the figure is 40 cm, find the area of the shaded region. [Use π = \(\frac{22}{7}\)] (2015D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 34
    Solution:
    OA = OB …[Given
    Let OA = OB = r
    AO is the diameter of small semicircle
    ∴ Radius of small semicircle, R = \(\frac{AO}{2}\) = \(\frac{r}{2}\)
    BO is the radius of big semicircle, r
    Total perimeter = Perimeter of small semi-circle + Perimeter of big semi-circle + OB
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 35

    Question 22.
    In Figure, O is the centre of a circle such that diameter AB = 13 cm and AC = 12 cm. BC is joined. Find the area of the shaded region. (Take π = 3.14) (2016OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 36
    Solution:
    ∠ACB = 90° …[Angle in a semi-circle
    ∴ AC2 + BC2 = AB2 …[Pythagoras’ theorem
    (12)2 + BC2 = (13)2
    144 + BC2 = 169
    BC2 = 169 – 144 = 25
    BC = + 5 cm
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 37

    Question 23.
    In Figure, are shown two arcs PAQ and 0 PBQuestion Arc PAQ is a part of circle with centre O and radius OP while arc PBQ is a semi-circle drawn on PQ as diameter with centre M. If OP = PQ = 10 cm, show that area of shaded region is 25(\(\sqrt{3}=\frac{\pi}{6}\))cm2. (2016D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 38
    Solution:
    OP = OQ = 10 cm (Tangents drawn from an external point are equal
    PQ = 5 + 5 = 10 cm
    OP = OQ = PQ = 10 cm … [sides are equal
    ∴ ∆POQ is an equilatral ∆.
    ⇒ ∠POQ = 60° …[Angles of an equilateral ∆
    Side = 70 cm, r = 5 cm, θ = 60°, R = 10 cm
    Area of the shaded region = Area of ∆OPQ + Area of Semi-circle(PBQM) – Area of sector (OPAQ)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 38

    Question 24.
    In Figure, O is the centre of the circle with AC = 24 cm, AB = 7 cm and ∠BOD = 90°. Find the area of the shaded region. (Use π = 3.14) (2012OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 39
    Solution:
    ∠BAC = 90° …[Angle in a semi-circle
    Int rt. ∆BAC,
    BC2 = AC2 + AB2 …(Pythagoras’ theorem
    = 242 + 72
    = 576 + 49 = 625
    BC = \(\sqrt{625}\) = 25 cm
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 40

    Question 25.
    In Fig., AB and CD are two diameters of a circle with centre 0, which are perpendicular to each other. OB is the diameter of the smaller circle. If OA = 7 cm, find the area of the shaded region. (Use π = \(\frac{22}{7}\)) (2013D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 41
    Solution:
    Here, r = 7/2 cm, R = 7 cm
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 42

    Question 26.
    In Figure, APB and CCD are semi-circles of diameter 7 cm each, while ARC and a BSD are semi-circles of diameter 14 cm each. Find the perimeter of the shaded region. [Use π = \(\frac{22}{7}\)] (2011D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 43
    Solution:
    BC = R = 7 cm
    AB = r = \(\frac{7}{2}\)cm
    The perimeter of the shaded region
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 44

    Question 27.
    In Figure, ABCD is a trapezium of area 24.5 sq. cm. In it, AD || BC, ∠DAB = 90°, AD = 10 cm and BC = 4 cm. If ABE is a quadrant of a circle, find the area of the shaded region. [Take π = \(\frac{22}{7}\)] (2014OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 45
    Solution:
    ar (trapezium) = 24.5 cm2 … [Given
    = \(\frac{1}{2}\)(AD + BC) × AB = 24.5 …(i)
    = (10 + 4) × AB = 24.5 × 2
    = 14.(AB) = 49
    AB = \(\frac{49}{14}\) = \(\frac{7}{2}\) cm = r
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 46

    Question 28.
    Find the area of the minor segment of a circle of radius 14 cm, when its central angle is 60°. Also find the area of the corresponding major segment. [Use π = \(\frac{22}{7}\)] (2015OD)
    Solution:
    Here, r = 14 cm, θ = 60°
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 47
    Area of major segment = Area of circle – Area of minor segment
    = 616 – 17.9 = 598.10 cm2 (Approx.)

    Question 29.
    Find the perimeter of the D shaded region in Figure, if ABCD is a square of side 14 cm and APB and CPD are semicircles. [Use π = \(\frac{22}{7}\)] (2011OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 48
    Solution: Perimeter of the shaded region
    = Circumference of circle + AD + BC
    = 2πr + 14 + 14
    = 2 × \(\frac{22}{7}\) × 7 + 28 ….[. r = \(\frac{14}{2}\) = 7 cm
    = 44 + 28 = 72 cm

    Question 30.
    In Figure, OABC is a square of side 7 cm. If OAPC is a quadrant of a circle with centre O, then find the area of the sha- o ded region. [Use π = \(\frac{22}{7}\)] (2012D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 49
    Solution:
    Area of shaded region = Area of Square – Area of Quadrant
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 50

    Question 31.
    In Figure ABCD is a square of side 4 cm. A quadrant of a circle of radius 1 cm is drawn at each vertex of the square and a circle of diameter 2 cm is also drawn. Find the area of the shaded region. (Use π = 3.14) (2012OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 51
    Solution:
    Area of 4 quadrants (a circle)
    = 4 × \(\frac{1}{4}\)π(1)2
    = π sq.cm
    Area of the square = (4)2 sq.cm = 16 sq.cm
    Area of the circle at the centre = π(r)2 = π(1)2
    = π sq.cm
    ∴ Area of shaded portion
    = Area of square – 2 (Area of circle)
    = 16 – (11 + r) sq.cm
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 52

    Question 32.
    From a rectangular sheet of paper ABCD with AB = 40 cm and AD = 28 cm, a semi-circular portion with BC as diameter is cut off. Find the area of the remaining paper. (Use π = \(\frac{22}{7}\)) (2012OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 53
    Solution:
    Length of paper,
    AB, l = 40 cm
    Width of paper,
    AD, b = 28 cm
    Area of paper = l × h
    = 40 × 28 = 1120 sq. cm
    Diameter of semi-circle = 28 cm …(i)
    Radius of semi-circle, r = 14 cm
    Area of semi-cirice = \(\frac{1}{2} \pi r^{2}=\frac{1}{2} \times \frac{22}{7} \times 14 \times 14\)
    = 308 sq.cm …(ii)
    ∴ Area of remaining paper = 1120 – 308
    = 812 sq.cm

    Question 33.
    In Figure, find the area of the shaded region, if ABCD is a square of side 14 cm and APD and BPC are semi-circles. (2012OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 54
    Solution:
    Side (diameter) = 14 cm
    ∴ radius, r = 7 cm
    Area of shaded region
    = ar(Square) – 2ar(semi-circle)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 55

    Question 34.
    In Figure, find the area of the shaded region. [Use π = 3.14] (2015D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 56
    Solution:
    Let the side of big square = A = 14 cm
    Let the radius of circle,
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 57
    ∴ Required area = (Area of big square – Area of small square – Ar. of 4 semicircles)
    = (196 – 16 – 25.12) cm2
    = 154.88 cm2

    Question 35.
    All the vertices of a rhombus lie on a circle. Find the area of the rhombus, if the area of the circle is 1256 cm2. [Use π = 3.14] (2015OD)
    Solution:
    Let r be the radius of circle
    In rhombus, AB = BC = CD = AD
    ⇒ AC = BD = 2r
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 58

    Question 36.
    In Figure, ABCD is a square of side 14 cm. Semi-circles are drawn with each side of square as diameter. Find the area of the shaded region. [Use π = \(\frac{22}{7}\)] (2016D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 59
    Solution:
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 60
    Area of shaded region
    = 2(Area of square) – 4(Area of semicircle)
    = 2 × 196 – 308 = 392 – 308 = 84 cm2

    Areas Related to Circles Class 10 Important Questions Long Answer (4 Marks)

    Question 37.
    In Figure, arcs are drawn by taking vertices A, B and C of an equilateral triangle ABC of side 14 cm as centres to intersect the sides BC, CA and AB at BZ their respective mid-points D, E and F. Find the area of the shaded region. [Use π = \(\frac{22}{7}\) and \( \sqrt{{3}} \) = 1.73] (2011D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 61
    Solution:
    ∠ABC = ∠BAC = ∠ACB = 60° … [equilateral ∆
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 62

    Question 38.
    Find the area of the shaded region in Figure, where arcs drawn with centres A, B, C and D intersect in pairs at mid-points P, Q, R and S of the sides AB, BC, CD and DA respectively of a square ABCD, where the length of each side of square is 14 cm. (Use π = \(\frac{22}{7}\)) (2011D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 63
    Solution:
    Side = 14 cm, radius, r = \(\frac{14}{2}\) = 7 cm
    Area of the shaded region
    = ar (square) – 4 (ar of quadrant)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 64

    Question 39.
    In Figure, three circles each of radius 3.5 cm are drawn in such a way that each of them touches the other two. Find the area enclosed between these three circles (shaded region). [Use π = \(\frac{22}{7}\)] (2011OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 65
    Solution:
    AB = BC = CA
    = 2(3.5) = 7 cm
    ∴ ∆ABC is an equilateral ∆
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 66

    Question 40.
    Find the area of the shaded region in Figure, where ABCD is a square of side 28 cm. (2011OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 67
    Solution:
    Here r = \(\frac{28}{4}\) = 7 cm
    Area of the shaded region
    = ar(square) – 4(circle)
    = (side)2 – 4 (πr2)
    = (28)2 – 4 × \(\frac{22}{7}\) × 7 × 7 = 784 – 616 = 168 cm2

    Question 41.
    In Figure, an equilateral triangle has been inscribed in a circle of radius 6 cm. Find the area of the shaded region. [Use π = 3.14] (2011OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 68
    Solution:
    Here θ = \(\frac{360}{3}\) = 120°, r = 6 cm
    Area of shaded region
    = 3(ar of minor segment) = 3[ar(minor sector) – ar(∆ABC)] Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 69
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 70

    Question 42.
    In Figure, ABC is a right-angled triangle right angled at A. Semicircles are drawn on AB, AC and BC as diametres. Find the area of the shaded region. (2013D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 71
    Solution:
    In rt. ∆BAC,
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 72
    ∴ BC2 = AB2 + AC2 …[Pythagoras’ theorem
    = (3)2 + (4)
    = 9 + 16 = 25 cm2
    ∴ BC = +5 cm … [Side of ∆ can’t be -ve
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 73
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 74

    Question 43.
    In Figure, PQRS is a square lawn with side PQ = 42 metres. Two circular flower beds are there on the sides PS and QR with centre at O, the inter- section of its diagonals. Find the total area of the two flower beds (shaded parts). (2015OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 75
    Solution:
    PO = 42 m …[Given
    PS = QR …[∵ side of square
    OR = OP …[Radius of circle
    Let OR be the radius of circle = x
    So, PR = OR + OP = 2x
    Using Pythagoras’ theorem,
    ⇒(PR)2 = (RQ)2 + (PQ)2
    ⇒(2x)2 = (42)2 + (42)2
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 76

    Question 44.
    An elastic belt is placed around the rim of a pulley of radius 5 cm. (given figure) From one point C on the belt, the elastic belt is pulled directly away from the centre o of the pulley until it is at P, 10 cm from the point O. Find the length of the belt that is still in contact with the pulley. Also find the shaded area. (Use π = 3.14 and \(\sqrt{3}\) = 1.73) (2016D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 77
    Solution:
    ∠OAP = 90° ….[Tangent is ⊥ to the center through the point of contact
    In rt. ∆OAP,
    Cos θ = \(\frac{\mathrm{OA}}{\mathrm{OP}}=\frac{5}{10}=\frac{1}{2}\) = cos 60°
    ∴ θ = 60°
    ∠AOB = 60° + 60° = 120° …(i)
    Reflex ∠AOB = 360° – ∠AOB
    = 360° – 120° = 240°
    α = 240° …[Let Reflex ∆AOB = α
    The length of the belt that is still in contact with the pulley = ADB = lenght of major arc
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 78
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 79

    Question 45.
    In Figure, is shown a sector OAP of a circle with centre 0, containing ∠θ. AB is a perpendicular to the radius OA and meets OP produced at B. Prove that the perimeter of shaded region is r [tan θ + sec θ + \(\frac{\pi \theta}{180^{\circ}}\) – 1] (2016OD)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 80
    Solution:
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 81

    Question 46.
    In the Figure, the side of square is 28 cm and radius of each circle is half of the length of the side of the square where 0 and Oare centres of the circles. Find the area of shaded region. (2017D)
    Important Questions for Class 10 Maths Chapter 12 Areas Related to Circles 82
    Solution:
    Side = 28 cm, Radius = \(\frac{28}{2}\) cm = 14 cm
    The area of the shade = Area of square + \(\frac{3}{4}\) (Area of circle) + \(\frac{3}{4}\) (Area of circle)
    = Area of square + \(\frac{3}{2}\) (Area of circle) …[Area of square = (Side)2; Area of circle = πr2
    = (28)2 + \(\frac{3}{2}\) × \(\frac{22}{7}\) × 14 × 14
    = 784 + 924 = 1708 cm2

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