Question

how do you find the height of an unknown building?I need help setting upo the formula.

Answer 1

Do you have more details or are you supposed to come up with the whole thing yourself?

The easiest on is to use the kinematic equation:
\[d=v_i t + \frac{1}{2} a t^2\]
What you do is drop a ball from rest at the top of the building and use a clock to time when it hits the ground. Since it is dropped from rest, the initial velocity v=0 and the acceleration is just gravity a=9.81 m/s^2. Since your clock measured t, you can plug in the values to get d which is the height of the building.

Answer 2

There is a legendary joke about this problem. One form is:
Bob Pease (Nat.Semi.) records the story of the Physics student who
got the following question in an exam:

"You are given an accurate barometer, how would you use it
to determine the height of a skyscraper ?"

1: He answered: "Go to the top floor, tie a long piece of string to the
barometer, let it down 'till it touches the ground and measure the
length of the string".

The examiner wasn't satisfied, so they decided to interview the guy:

"Can you give us another method, one which demonstrates your knowledge
of Physics ?"

2: "Sure, go to the top floor, drop the barometer off, and measure how
long before it hits the ground......"

"Not, quite what we wanted, care to try again ?"

3: "Make a pendulum of the barometer, measure its period at the bottom,
then measure its period at the top......"

"..another try ?...."

4: "Measure the length of the barometer, then mount it vertically on the
ground on a sunny day and measure its shadow, measure the shadow of the
skyscraper....."

"....and again ?...."

5: "walk up the stairs and use the barometer as a ruler to measure the
height of the walls in the stairwells."

"...One more try ?"

6: "Find where the janitor lives, knock on his door and say 'Please, Mr
Janitor, if I give you this nice Barometer, will you tell me the height
of this building ?"

Source and the other version:
http://jcdverha.home.xs4all.nl/scijokes/2_12.html#subindex

Answer 3

Or you could start with your back to the building and walk away from it, say, one hundred metres. Then sight the top of the building along a ruler held against a protractor and measure the angle to the top of the building, call that (theta). The height of the building is (your height) + 100. tan(theta).