Question

A thread is wound 200 times round a reel of diameter 5 cm. Use the value 3 for it to find the approximate length of the thread in metres.
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Answer 1

Answer:

Length of the thread = 30 metres

Step-by-step explanation:

Length of the thread in one round of a reel = Circumference of the reel

                                                                    C = $2\pi r$

Since radius of the reel = $\frac{\text{Diameter}}{2}$

                                       = $\frac{5}{2}$

                                       = 2.5 cm

Circumference of the reel = 2(π)(2.5)

                                           = 5π

                                           = 5×3

                                           = 15 cm

Length of the thread wound in one round around the reel = 15 cm

Since, thread is wound 200 times round a reel, length of the thread

= 200 × 15                                                      

= 3000 cm

≈ 30 metres

Therefore, Option (B) will be the answer.