# Time for an object to fall

1. Apr 25, 2010

### jamesd2008

Hi,

If you no the height of an object only, assuming no frictional forces, and that it is on earh. Can you determine how long it will take to hit the ground?

Thanks
James

2. Apr 25, 2010

### jamesd2008

Also the final velocity is also unknown and the initial velocity is zero?

3. Apr 25, 2010

### karkas

I am assuming that you're talking about the height between the object and the floor. The answer is yes, and that is obvious from the equations that describe free fall, meaning the fall that is induced and preserved only by the force of gravitational attraction that the earth exerts on the body.

So we have
$h = \frac{1}{2} g t^2 \Leftrightarrow t = \sqrt{\frac{2h}{g}}$
and since you know h, you can calculate the required time. Using that t you can solve for the final velocity of the body, the one it has right before it reaches ground. And yes, since you let the body go at one point without pushing it downwards, the initial velocity is zero.

Last edited: Apr 26, 2010
4. Apr 25, 2010

### morrobay

No t=square root (2h/g)
velocity = square root (2gh)

5. Apr 26, 2010