A string around the earth will be 25000 miles long. ?

Question

raise the string 1 foot,how much longer is string

Answer 1

Call the circumference c and the radius r:

dc/dr = d(2 pi r)/dr = 2 pi

So the increase will be 2 pi feet = 6.28 ft

Answer 2

Linlyons is right. The string will have to be 6.2 feet longer.

Answer 3

2pi*r = 25000

r=3978.87

R = r+1 = 3979.87

2pi*R = 25006

Answer 4

2 pi longer.

circumference = 2 pi R

increase R by 1 and the difference is 2 pi.