A wheel completes 21000 revolutions covering a distance of 66 km. Find the radius of the wheel.

Correct option is D

Given:

Number of revolutions = 21000

Distance covered = 66 km = 66000 meters

Formula Used :

Distance covered in one revolution = Circumference of the wheel = 2$$\pi$$$$\times$$​radius

Total distance covered = Number of revolutions $$\times$$ Circumference​

Solution:

Let the radius of the wheel be 'r' meters.

Circumference = 2$$\pi$$​r

Total distance covered = Number of revolutions$$\times$$​Circumference

66000 = 21000 $$\times$$2$$\pi$$​​r​

66000 = 42000 $$\times \pi$$​r

r = $$\frac{66\times 7}{42 \times 22}$$​ = $$\frac12$$ m​