Lethal Jump Heights?

[RVJ]

This summer I went out cliff-jumping with a couple of friends. The cliffs we went to (known as pulpit rock, located in Lake Placid, New York) had different heights to jump from. There was the 19ft cliff, 24ft, 40ft, 50ft, and 60ft. It got me thinking... what's the maximum safest height to jump from (assuming you land in the water correctly)? I ended up jumping the 50ft after MUCH deliberation, and the impact on the water didn't feel bad at all.

[imatfaal]

 

The La Quebrada Cliffs are famous for the diving there - about 125 feet

 

 

Record breaking good Dive of 174 feet

 

 

World Record is over 175 feet - but not aesthetically as good

[JohnB]

The other point is terminal velocity.

 

IIRC this would be about 185 mph for a jumper or diver. What is the minimum height to achieve this speed? Jumping from a higher point won't make you land any faster.

 

You could also adopt the skydiver spreadeagle pose for most of the way down, reducing the terminal velocity to about 120 mph and change to feet first at the last moment. Either way it will still hurt and possibly push your feet up to somewhere around your lower spine.

[imatfaal]

185 mph = 82.7 m/s

 

[math] v^2 = u^2 + 2as[/math]

 

v -> final velocity 82.7m/s

u-> initial velocity 0m/s

a-> acceleration 9.8m/s^2

s-> distance - unknown

 

[math] \frac{v^2 - u^2}{2a} = s[/math]

 

s= 349 metres

[John Cuthber]

In classical physics, you never (quite) reach the terminal velocity.

Imatfall's maths shows over what distance you would reach that speed in a vacuum, but terminal velocity is only defined if there is an atmosphere.

[JohnB]

True John.

 

The thing is that we now know that after the first thousand feet it makes no difference. Fall 1,000 feet or 20,000 feet, you hit at the same speed.

 

Even so it still makes the story of Nicholas Alkemade astonishing. And yes, the German Authorities did give him a certificate, signed by the German Kommandant and the ranking British and American officers.