Question

The second on a watch is 14mm long. What area does it sweep through in 30 seconds

Answer 1

Exact Area = 98pi  

Approximate Area = 307.8760800518 (use calculator stored version of pi)

Approximate Area = 307.72 (using pi = 3.14)

Units are in square millimeters

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Explanation:

In 60 seconds, the hand sweeps out a full circle of radius 14. The area of this circle is

A = pi*r^2 = pi*14^2 = 196pi

Half of this is what the hand sweeps out in 30 seconds, so A/2 = (196pi)/2 = 98pi is the exact area it sweeps out. Your calculator would then show 98pi = 307.8760800518 approximately

If instead you use pi = 3.14, then the approximate area is 98*3.14 = 307.72