# Finding distance to an object if it's height is known

• Oct 6th 2009, 10:54 AM
jonnyknowsbest
Finding distance to an object if it's height is known
I am sorry if this is in the wrong topic, but i am trying to find a formula for the following:

I know that the height of a golf flag is 84 inches. From where i am standing, the flag appears to be 0.75 inches tall. How far away is the flag?

Any / all help is appreciated

Regards

Jonathan
• Oct 6th 2009, 01:12 PM
aidan
Quote:

Originally Posted by jonnyknowsbest
I am sorry if this is in the wrong topic, but i am trying to find a formula for the following:

I know that the height of a golf flag is 84 inches. From where i am standing, the flag appears to be 0.75 inches tall. How far away is the flag?
Any / all help is appreciated
Regards
Jonathan

To give a valid answer, it is necessary to know how far from your eye the 0.75" measurement happens to be.

However, I'll make some assumptions:
1) you are holding a penny (a penny is 19 mm diameter which is almost 3/4 inch) at arms length;
your arm is 3 feet in length.

Converting all to feet:
0.75" is 0.75/12 feet or 0.0625 feet.

3 feet is to 0.0625 feet as some unknown distance x is to 84 inches (84/12 is 7 feet)

$\dfrac{3}{0.0625} = \dfrac{x}{7}$

$\dfrac{3 \times 7}{0.0625} = x$ = 336 feet.

If the assumptions are not correct, then the results probably aren't either.