Mensuration
- The perimeter (in metres) of a semicircle is numerically equal to its area (in square metres). The length of its diameter is (take π = 22/7)
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Using Rule 14,
Let the radius of the semi – circle ber metre.
According to the question, πr + 2r = πr²= π + 2 = × πr² ⇒ 2π + 4 = πr 2 r = 2π + 4 = 2 + 4 = 2 + 28 = 2 + 14 = 36 π π 22 11 11 ∴ Diameter = 2 × 36 = 72 = 6 6 metres 11 11 11 Correct Option: C
Using Rule 14,
Let the radius of the semi – circle ber metre.
According to the question, πr + 2r = πr²= π + 2 = × πr² ⇒ 2π + 4 = πr 2 r = 2π + 4 = 2 + 4 = 2 + 28 = 2 + 14 = 36 π π 22 11 11 ∴ Diameter = 2 × 36 = 72 = 6 6 metres 11 11 11
- The ratio of the numbers giving the measure of the circumference and the area of a circle of radius 3 cm is
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Using Rule 14,
Circumference of circle= 2πr
= 2π × 3 = 6π cm
Area of circle = πr² = π × 3 × 3 = 9π cm²
∴ Required ratio = 6π : 9π= 2 : 3Correct Option: B
Using Rule 14,
Circumference of circle= 2πr
= 2π × 3 = 6π cm
Area of circle = πr² = π × 3 × 3 = 9π cm²
∴ Required ratio = 6π : 9π= 2 : 3
- The ratio of the radii of two wheels is 3 : 4. The ratio of their circumference is
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Tricky Approach
Ratio of the circumference = Ratio of radii = 3 : 4Correct Option: B
Tricky Approach
Ratio of the circumference = Ratio of radii = 3 : 4
- The length (in cm) of a chord of a circle of radius 13 cm at a distance of 12 cm from its centre is
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AC = √13² - 12² = √169 - 144
= √25 =5 cm
∴ AB = 10 cmCorrect Option: C
AC = √13² - 12² = √169 - 144
= √25 =5 cm
∴ AB = 10 cm
- The diameter of a wheel is 98 cm. The number of revolutions in which it will have to cover a distance of 1540 m is
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Using Rule 7,
Distance covered by wheel in one revolution = circumference of the wheel= π × diameter = 22 × 98 = 308 cm 7 ∴ Number of revolutions = 1540 × 100 = 500 308 Correct Option: A
Using Rule 7,
Distance covered by wheel in one revolution = circumference of the wheel= π × diameter = 22 × 98 = 308 cm 7 ∴ Number of revolutions = 1540 × 100 = 500 308