by webnelly

*Question by Hannah*: How long will it take for someone to land after jumping off a forty foot ledge?

i went cliff diving and i’m not sure how high i jumped. i counted as someone else jumped and it was about 5 seconds. so, i want to know a) how long it would take a 120 pound person to land after jumping 40 feet, no gear or anything? b) how fast would they be falling? and c) how high would someone have jumped if it took 5 seconds to land?

the 5 seconds i counted weren’t perfect seconds so that’s why i want to know a) and b).

**Best answer:**

*Answer by Jon*

Oh dear this is a physics problem not diving! I’ll be honest with you, I just started taking physics but ill try and help you to the best of my knowledge (you may want to double check my reasoning with someone more familiar with physics).

My physics isn’t good enough to calculate jumping off a cliff (somebody else might be able to do this) so the following is assuming you STEPPED off the cliff NOT jumped.

a) Your weight wont matter, because when you step off a cliff your in free fall. In free fall everything accelerates at roughly 10 meters per second. Galileo did some experiment where he dropped two different weighted objects from the same height. They hit the ground at the same time. Therefore it should take anyone the same time as that 5 seconds guy you counted.

b) You accelerate the longer your in free fall. So I couldn’t tell you how fast they would be falling because the speed is constantly changing. But i can tell you this: In freefall, assuming the only force that acting on you is gravity, (air resistance not counted), you accelerate at 10 meters per second. It is possible to calculate speed at a given point while in free fall, but my physics isn’t good enough to do that.

c) I would like to help you hear but again I don’t know the math involved for jumping.

I hope this helps a little at least.

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