1. Dec 16, 2003

### celect

I need to know where to start, any good books to help out I'm taking a self study course. I have some study guide from Army education center. I am waiting for video course show up.

How long would it take for an object dropped from the Leaning Tower
of Pisa height 54.6 meters to hit the ground?

Thanks

2. Dec 16, 2003

### himanshu121

u need to certain equations while solving kinematics problem

here we have to connect displacement and time so the equation is

$$x= x_0 + v_0t+(1/2)at^2$$

3. Dec 17, 2003

### celect

Physics 101

I guess I should have mentioned that this is my first taking a physics course.

I reviewed the text and came up with the folowing.

t=d/v ave

54.4/9.8m/s^2

I came up with 17.4 seconds.

4. Dec 17, 2003

### himanshu121

Apply the formula which i have quoted i.e.
$$x= x_0 + v_0t+(1/2)at^2$$

here x-x_0= - 54.4
v_0=0
a=-g

5. Dec 17, 2003

### chroot

Staff Emeritus
Re: Physics 101

This formula could be used, but to use it, you'd first have to find $v_{\text{average}}$, which is actually rather difficult to find.

Futhermore, note that $9.8 m/s^2$ is not a velocity, it's an acceleration. If you were to blindly perform this calculation, dividing "meters" by "meters per second squared," your anwer will be in "seconds squared" -- which is not the same as "seconds" at all!

You should take himanshu's advice -- he is trying to teach you how to use the proper formula for the job.

- Warren

6. Dec 17, 2003

### celect

Thanks to all

by himanshu121
Apply the formula which i have quoted i.e.
x= x_0 + v_0t+(1/2)at^2

here x-x_0= - 54.4
v_0=0
a=-g

My text only includes a few formulas.
This is my first course I learning distance study.
this one looks like yours.

d = v_i * t + 1/2 * a * t^2

I used this formula:
given v_i =0.0m/s
d= -54.6m
a= -9.8m/s^2

I have to find t

I now solve t= 3.3 s

(thanks I read more now I understand to use - for doward motion)

7. Dec 17, 2003

### himanshu121

Yes its correct and is good u got the meaning for - sign

Last edited: Dec 17, 2003
8. Dec 19, 2003

### ShawnD

Integrate the velocity formula to get a distance formula

$$\int V_f \,dt = \int V_i + at \,dt$$

$$d_f = d_i + \frac {1}{2} at^2$$

now rearrange

$$\sqrt{\frac{2(d_f - d_i)}{a}} = t$$

$$\sqrt{\frac{2(54.6 - 0)}{9.81}} = 3.336s$$

3.336 s