Chapter 14 A: MENSURATION









  1. Explanation :

    Let hypotenuse = x cm
    Then, by Pythagoras theorem:
    x2 = (48020)2 + (36015)2
    x so 60025 cm




  1. Explanation :

    Let one side of the △ be = a Perimeter of equilateral triangle = 3a 3a = 72\( \sqrt{3} \) = a = 24\( \sqrt{3} \) cm Height = AC; by Pythagoras theorem AC2 = a2 – (a/2)2 AC = 36 cm





  1. Explanation :

    Let inner radius = A; then 2pr = 440 so p = 70
    Radius of outer circle = 70 + 14 = 84 cm
     Outer diameter = 2 × Radius = 2 × 84 = 168




  1. Explanation :

    Let inner radius = r and outer radius = R
    Width = R – r = 396/2π - 352/2π
    so (R – r) = 44/2π = 7 meters




  1. Explanation :

    Let outer radius = R; then inner radius = r = R – 7
    2pR = 220 so 35m;
    r = 35 – 7 = 28 m
    Area of torch = pR2 – pr2 p(R2 – r2) = 1386 m2
    Cost of traveling it = 1386 × = ` 693




  1. Explanation :

    Circumference of circle = 2pr = 44
    = r = 7 cm
    Area of a quadrant = π * r2 / 4 = 38.5 cm2




  1. Explanation :

    Volume of soil removed = l × b × h
    = 7.5 × 6 × 1.5 = 67.5 m3




  1. Explanation :

    The longest pole can be placed diagonally (3-dimensional) mensuration BC = \( \sqrt{18^2 + 24^2} \)= 30 AC = \( \sqrt{30^2 + 16^2} \) = 34 m





  1. Explanation :

    (d)
    Let the common ratio be = x
    Then; length = 3x, breadth = 2x and height = x
    Then; as per question 3x * 2x * x = 1296 so 6x3 = 1296
    fi x = 6 m
    Breadth = 2x = 12 m




  1. Explanation :

    Data is inadequate as it’s not mentioned that what part of the cube is melted to form cylinder




  1. Explanation :

    (b)
    Let the common ratio be = x
    Then, length = 4x, breadth = 3x and height = 2x
    As per question;
    2(4x * 3x + 3x * 2x + 2x * 4x) = 8788
    2(12x2 + 6x2 + 8x2) = 8788 fi 52x2 = 8788
    fi x = 13
    Length = 4x = 52 cm




  1. Explanation :

    The total volume will remain the same, let the side of the resulting cube be = a. Then,
    63 + 83 + 103 = a3
    fi a = cube root of 1728 = 12 cm




  1. Explanation :

    Slant length = l = \( \sqrt{6^2 + 8^2} \)= 10 cm Then curved surface area = prl = p × 6 × 10 so 60p And total surface area = prl + pr2 so p((6 × 10) + 62) = 96p





  1. Explanation :

    Volume of a cone = π * r2 * h / 3
    Then;100p = π * r2 * 12 / 3 = fi r = 5 cm
    Curved surface area = prl
    l = √ h2 + r2 = √ 52 + 122 = 13
    then,prl = p × 13 × 5 = 65p cm2
    




  1. Explanation :

    (d)
    Let the radius of the two cones be = x cm
    Let slant height of 1st cone = 5 cm and
    Slant height of 2nd cone = 7 cm
    Then ratio of covered surface area = 5π / 7π = 5 : 7




  1. Explanation :

    Radius = π * r * l / π * l  = 2376 / 3.14 * 18 = 42 cm
    Diameter = 2 × Radius = 2 × 42 = 84 cm




  1. Explanation :

    Let the radius of cylinder = 1(r)
    Then the radius of cone be = 2(R)
    Then as per question = π * r2*h / π * R2*h / 3 = 3 * π * r2*h / π * R2*h
    so 3 : 4




  1. Explanation :

    The perimeter would remain the same in any case.
    Let one side of a square be = a cm
    Then a2 = 484 fi a = 22 cm \ perimeter = 4a = 88 cm
    Let the radius of the circle be = r cm
    Then 2pr = 88 fi r = 14 cm
    Then area = pr2 = 616 cm2




  1. Explanation :

    Let the radius of the circle be = p
    Then 2pr – 2r = 16.8 fi r = 3.92 cm
    Then 2pr = 24.6 cm




  1. Explanation :

    Let the radius of the wheel be = p
    Then 5000 × 2pr = 1100000 cm fi r = 35 cm




  1. Explanation :

    Let the slant height be = l
    Let radius = r
    Then v = π * r2 * h/3 = so r = √ 3v/πh = fi = 5 cm
    l = √(h2 + l2) = √(122 + 52) = 13 cm




  1. Explanation :

    In 4 days, the short hand covers its circumference
    4 × 2 = 8 times long hand covers its circumference
    4 × 24 = 96 times
    Then they will cover a total distance of:-
    (2 × p × 4)8 + (2 × p × 6)96 fi 3818.24 cm




  1. Explanation :

    Let the radius of the smaller sphere = r Then, the radius of the bigger sphere = R Let the surface area of the smaller sphere = 1 Then, the surface area of the bigger sphere = 4 Then, as per question \( \frac{4\pir^2}{4\piR^2} = 1/4 , r/R = 1/2 \) and hence volumes = \( \frac{4\pir^3}{3} * \frac{3}{4\pi(2r)^3} = 1/8 \)





  1. Explanation :

    Inner radius(p) = 9/2 = 4.5 cm
    Outer radius (R) = 10/2 = 5 cm
    Volume of metal contained in the shell =  4πR3 – 4πr3 = 141.9
    fi 141.9 cm3




  1. Explanation :

    Let smaller radius (r) = 1
    Then bigger radius (R) = 2
    Then, as per question
    4πR2 / 4πr2 = (1/2)2 = 1 : 4




  1. Explanation :

    As per question 4πr3/3 = πr2h / 3 = 4r




  1. Explanation :

    Volume of wall = 1200 × 500 × 25 = 15000000 cm3
    Volume of cement = 5% of 15000000 = 750000 cm3
    Remaining volume = 15000000 – 750000 = 14250000 cm3
    Volume of a brick = 25 × 12.5 × 7.5 = 2343.75 cm3
    Number of bricks used = 14250000 / 2343.75 = 6080




  1. Explanation :

    Let the inner radius = r
    Then 2pr = 352 m. Then r = 56
    Then outer radius = r + 7 = 63 = R
    Now,pR2 – pr2 = Area of road
    = p(R2 – r2) = 2618 m2




  1. Explanation :

    1 hectare = 10000 m2
    Height = 10 cm = 1/10m
    Volume = 10000 × 1/10 = 1000 m3




  1. Explanation :

    Total surface area of 7 cubes so 7 × 6a2 = 1050
    But on joining end to end, 12 sides will be covered.
    So there area = 12 × a2 so 12 × 25 = 300
    So the surface area of the resulting figure = 1050 – 300 = 750




  1. Explanation :

    Let the rise in height be = h
    Then, as per the question, the volume of water should be equal in both the cases.
    Now, 90 × 40 × h = 150 × 8
    h = 150*8 / 90*40 = 1/3m = 100/3cm
    = 33.33 cm




  1. Explanation :

    Slant height (l) = √(72 + 242)= 25 m
    Area of cloth required = covered surface area of cone = prl = 22/7 × 7 × 25 = 550 m2
    Amount of cloth required = 550/5 = 110 m




  1. Explanation :

    If the ratio of their diameters = 2 : 1, then the ratio of their radii will also be = 2 : 1
    Let the radii of the broader cone = 2 and height be = 1
    Then the radii of the smaller cone = 1 and height be = 2
    Ratio of volumes = (π22*1 / 3) / (π12*2 / 3)
    = 4π/3 * 3/2π = 2 : 1




  1. Explanation :

    Area of base = 6 × 10 = 60 m2
    Volume of tent = 30 × 10 = 300 m3
    Let the radius be = r, height = h, slant height = l
    pr
    2 = 60 fi r = √(60/π)
    300 = πr2h/3 = 900 = p *60/π* h = h = 15 m




  1. Explanation :

    Volume of wood used = External volume – Outer Volume
    fi (10 × 8 × 6) – (10 – 1) × (8 – 1) × (6 – 1)
    fi 480 – (9 × 7 × 5) = 165 cm2
    




  1. Explanation :

    Total volume in both the cones will be equal. Let the number of smaller cubes = x
    x * 33 = 24 × 9 × 8 fi x = 24*72/27 = 64




  1. Explanation :

    Let one side of the cube = a
    Then a3 = 216 fi a = 6 m
    Area of the resultant figure
    = Area of all 3 cubes – Area of covered figure
    fi 216 × 3 – (4 × a2) fi 648 – 144 fi 504 m2




  1. Explanation :

    Volume of metal used = 4πR3/3 - 4πr3/3
    = 4π/3(123 – 103)
    = 3047.89 cm3
    Weight = volume × densityfi 4.9 × 3047.89
    fi 14942.28 gm




  1. Explanation :

    Volume of cube = 7
    3 = 343 cm3
    Radius of cone = 7/2 = 3.5 cm
    Height of cone = 7
    Ratio of volumes = πr2h/3/343 = 11:42
    




  1. Explanation :

    The volume in both the cases will be equal. Let the height of cone be = h
    4 × 22/7 × (14)3 × 1/3 = 22/7 * h/3 * (35/2)2
    so 4(14)3 = h(35/2)2 = h = 35.84 cm




  1. Explanation :

    Diameter of circle = diagonal of square
    = √(102 + 102)= 10√2
    ◊.◊ Radius = 5√2
    Area of circle = pr2 = 50p = 50 × 3.14 = 157.14 cm3
    




  1. Explanation :

    Area of triangle = rS; where r = inradius S = 15+8+7/2 = 20 cm △ = \( \sqrt{s(s-a)(s-b)(s-c)} \) △ = 60 cm2 Area of triangle = rS; r = 3 cm





  1. Explanation :

    Circumference of the circular face of the cylinder = 2pr
    fi 2 × 22/7 × 35/100 = 2.2 m
    Number of revolutions required to lift the bucket by 11 m = 11/2.2 = 5




  1. Explanation :

    Surface area of the cube = 6a2 = 6 × (20)2
    = 2400
    Area of 6 circles of radius 10 cm = 6pr2
    = 6 × p × 100
    = 1885.71
    Remaining area = 2400 – 1884 = 514.28




  1. Explanation :

    x * y * z = lb × bh × lh = (lbh)2
    (V) Volume of a cuboid = lbh
    So V2 = (lbh)2 = xyz
    




  1. Explanation :

    Diameter of the circle = diagonal of rectangle
    = √(82 + 62) = 10 cm
    Radius = 10/2 = 5 cm
    Area of shaded portion = pr2 – lb = 3.14 × 52 – 8 × 6
    = 30.57 cm2




  1. Explanation :

    Larger Radius (R) = 14 + 7 = 21 cm
    Smaller Radius (r) = 7 cm
    Area of shaded portion πR2θ/360 – πR2θ/360
    π*θ/360 (212 - 72) = 102.67 cm




  1. Explanation :

    Area of quadrilateral = Area of right angled triangle + Area of equilateral triangle x = √(202 - 122)
    = 16
    Area of quadrilateral = 1/2*16*12 + √3/4 × 20 × 20
    = 269 units2
    




  1. Explanation :

    h = √(242 - 132) = √407
    volume = Area of base * height/3 = 18*26*√407/3 = 156√407




  1. Explanation :

    The perimeter would remain the same in both cases. Circumference of circle = 2pr = 2 × 22/7 × 28
    = 176 cm
    Perimeter of square = 176
    Greatest side possible = 176/4 = 44 cm
    Length of diagonal = √(442 + 442) = 62.216
    = 88/2 * √2 = 44√2