Length of tape required to cover the edge of a semicircular disc of radius 10 cm is:

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62.8 cm

51.4 cm

31.4 cm

15.7 cm

answer is B.

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Detailed Solution

Given, a semicircular disc of radius 10 cm.
We know that a semicircle is just half a portion of a complete circle.
So, the circumference of the semicircle will be half that of the complete circle.
Now for a complete circle with ‘r’ radius, the circumference is given as

2 π r

So, we can say that apart from the circular portion, the circumference of a semicircle also includes the two radii or more exactly, the diameter of the semicircle.
Therefore, the circumference of a semicircle will be given as,

= 2 π r 2 + 2 r = π r + 2 r

The circumference of the semicircular disc is as follows,

= π r + 2 r = (3.14 × 10) + (2 × 10) = 31.4 + 20 = 51.4

Now, as the tape is to be covered all over the edges of this disc, the total length of the tape required will be the same as the circumference of the semicircular disc, i.e., 51.4 cm.
Hence, the correct option is (2).

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