# Time for an object to fall

1. ### jamesd2008

64
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. ### jamesd2008

64
Also the final velocity is also unknown and the initial velocity is zero?

3. ### karkas

125
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. ### morrobay

405
No t=square root (2h/g)
velocity = square root (2gh)

125