# Thread: Help with calculus question

1. ## Help with calculus question

Ok, so there are some questions in my class that, despite the fact that I understand how to do the basic problems reasonably well, I can't figure out how to apply in the harder problems. The problem below is a problem that I'm not even sure how to start...I would appreciate it if I could get some help in understanding how to do this problem. Thanks!

The equatorial radius of the earth is approximately 3960 miles. Suppose a wire is wrapped tightly around the earth at the equator. How much must this wire be lengthened if it is to be strung on poles 10 feet above the ground? (1 mile = 5290 feet).

2. Originally Posted by Missylovesmathz
Ok, so there are some questions in my class that, despite the fact that I understand how to do the basic problems reasonably well, I can't figure out how to apply in the harder problems. The problem below is a problem that I'm not even sure how to start...I would appreciate it if I could get some help in understanding how to do this problem. Thanks!

The equatorial radius of the earth is approximately 3960 miles. Suppose a wire is wrapped tightly around the earth at the equator. How much must this wire be lengthened if it is to be strung on poles 10 feet above the ground? (1 mile = 5290 feet).

As the perimiter of a circle of radius r is $2\pi r$ , the wire's length is $2\pi \cdot 3,960$.

After this I must say I don't understand what does "...it is to be strung on poles 10 feet above the ground" mean...

Tonio

3. Basically, you are increasing the radius by 10 feet. Incidentally, there are 5280 feet in one mile, not 5290.

4. Not counting catenary effects between poles, that is.