what is the height of the building?

Question

a stone is dropped from a top of a building of height 'h'. An observer from inside the building clocks the time for the stone to pass down a window as 0.2s. If the height of the window is 2m, find the height of the building. The bottom of the window is at a height 4m from the ground

Answer 1

The stone travels the 2 m of the window in 0.2 sec.

Its speed is 10 m /sec.

s = 9.81 m/sec² (t)

10 m/sec = 9.81 m/sec² t

10 = 9.81 /sec t

10 sec = 9.81 t

1.0193 ≈ t

 

This is the time needed for the stone to travel from the top of the building to the window. 

You can calculate the distance.

Answer 2

Hi Subha,

 

The key to this question is to find the displacement from of the stone from the top of the building to the window. We know that vertical displacement is given by the formula: y = -1/2gt^2+v_yt+y_0.

 

You are given the initial height, y_0 = h

The stone is not given an initial velocity (i.e. it is dropped not thrown downward), v_0 = 0

 

This leaves us with y = -1/2gt^2+h.

 

We know that at t = 0.2, y = 4 (the height of the window).

 

I hope this helps! This is not the final answer; you must solve for h.

 

-Anthony