Question

A test-tube has a diameter of 3cm,how many turns would a piece of thread of length 90.42 make round the test tube.(take pie22/7).

Answer 1

Given that,

Diameter = 3 cm

Length of thread = 90.42 cm

We need to calculate the circumference

Using formula of circumference

$c=2\pi r$

Where, r = radius of tube

Put the value into the formula

$c=2\pi\times\dfrac{3}{2}$

$c=9.42\ cm$

We need to calculate the number of turns

Using formula of number of turns

$N= \dfrac{l}{c}$

Where, l = length of thread

N = number of turns

c = circumference of tube

Put the value into the formula

$N=\dfrac{90.42}{9.42}$

$N=9.5$

Hence, The number of turns of thread will be nine and half.