Answer: just an extra one foot
Step-by-step explanation:
Given that the length of the piece of string = 25,000 miles
Since the string is long enough to exactly circle the globe at the equator over oceans, deserts and jungles. We can say that the string could completely circle a sphere
Assuming that the earth is a perfect sphere.
The circumference of the circle = 25,000 mile.
But note that the circumference of a circle is directly proportional to the radius. If you double the radius, the circumference will also be doubled. Half the circumference, half the radius. Increase the circumference by 30%, radius will also be increased by 30% and so on.
In this question, the radius is being increased by 3 feet, so we need to know that as a fraction of the original radius.
Circumference = 2πr
Let's also convert miles to feet
25000 × 5280 = 2(3.143)r
r = 132 × 10^6/2π
r = 21008452.5 feet
3 feet - that's how far off the ground we're lifting the string out of 21008452.5 feet is close to one part in 25000 miles. The string was 132000000 feet long to start with, so we need just an extra 1 foot.
