# B Time taken for free falling objects to travel a set distance

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1. Jun 14, 2016

### Jude Caird

The time taken for a free-falling object to fall a set distance (on earth) is, according to Wikipedia, described by the equation:

t = √(2d/g).

Why is the distance doubled in this equation/ how is this derived?

2. Jun 14, 2016

### axmls

Do you know any of the standard kinematics equations for a constant acceleration?

3. Jun 14, 2016

### Jude Caird

K = 1/2mv2?

4. Jun 14, 2016

### PeroK

5. Jun 14, 2016

### Jude Caird

Sorry for my ignorance.

6. Jun 14, 2016

### PeroK

Have you just picked up this formula from Wikipedia without any prior knowledge or are you learning some physics/kinematics?

7. Jun 14, 2016

### Jude Caird

I am interested in orbital mechanics etc. I have a suitable understanding of physics and kinematics and the formulae associated with gravity. I tried to derive the formula from my own knowledge, but failed.

8. Jun 14, 2016

### PeroK

You've never seen the equation $s = \frac{1}{2}at^2$ then?

9. Jun 14, 2016

### Jude Caird

no

10. Jun 14, 2016

### Jude Caird

Is that what it's derived from?

11. Jun 14, 2016

### PeroK

Yes, you could google for SUVAT or "kinematics". Or, try this:

http://www.examsolutions.net/maths-revision/mechanics/kinematics/suvat/derivation/tutorial-1.php [Broken]

Last edited by a moderator: May 8, 2017
12. Jun 14, 2016

### Jude Caird

Thank You

Last edited by a moderator: May 8, 2017