Question 56

A circular disc of area $$0.64\pi m^{2}$$ rolls down a length of 1.408 km. The number of revolutions it makes is:
(Taken $$\pi = \frac{22}{7}$$).

Solution

Area = $$\pi r^2$$

$$\pi r^2$$ = $$0.64\pi m^{2}$$

r = 0.8 m

Circumference of disc = $$2 \pi r = 2 \times (22/7) \times 0.8 = 5.02

Length = 1.408 km = 1408 m

The number of revolutions = 1408/5.02 = 280

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