Advertisements
Advertisements
Question
The circumference of a circle whose area is 81 πr2, is ______.
Options
9 πr
18 πr
3 πr
81 πr
Advertisements
Solution
The circumference of a circle whose area is 81 πr2, is 18 πr.
Explanation:
Let the radius of circle be R.
∴ Area of circle = πR2
⇒ 81πr2 = πR2
⇒ R = `sqrt(81r^2)`
⇒ R = 9r
Now, circumference = 2πR = 2π(9r) = 18πr
APPEARS IN
RELATED QUESTIONS
An elastic belt is placed round the rim of a pulley of radius 5 cm. One point on the belt is pulled directly away from the centre O of the pulley until it is at P, 10 cm from O. Find the length
of the belt that is in contact with the rim of the pulley. Also, find the shaded area.
The wheels of a car are of diameter 80 cm each. How many complete revolutions does each wheel make in 10 minutes when the car is traveling at a speed of 66 km per hour? [Use Π = 22/7]
Find the perimeter of a semicircular protractor whose diameter is 14 cm.
Find the curved surface area , the total surface area and the volume of a cone if its :
Height = 15 cm , radius = 8 cm
A conical tent with a capacity of 600 m3 stands on a circular base of area 160 m2 Find in m2 the area of the canvas.
Two circles touch each other externally. The sum of their areas is 5811 cm2 and the distance between their centres is 10 cm. Find the radii of the two circles.
The speed of the car is 66 km/hour. If each wheel of the car is 140 cm in diameter, find the number of revolutions made by each wheel per minute.
The diameter of two circles are 28 cm and 24 cm. Find the circumference of the circle having its area equal to sum of the areas of the two circles.
Find the circumference of the circles whose radii are given below.
91 mm
The diameters of front and rear wheels of a tractor are 80 cm and 2 m respectively. Find the number of revolutions that rear wheel will make in covering a distance in which the front wheel makes 1400 revolutions.
