Saturday, December 1, 2012

Base Jumpin’

By Allie Dyer

Base jumping is an activity where a person jumps off a high structure of
some kind with only a parachute to break their fall. In this video, this Russian base
jumper had some difficulty opening his parachute during this 120 meter fall. http://
www.youtube.com/watch?v=sJ59bNDhJcA
I wanted to know with what force he hit the initial snow and also how far
through the snow he travelled before stopping.

I assumed that it only took about .3 seconds to come to a complete stop from hitting
the initial snow.

V, or velocity, in this problem refers to the terminal velocity of the jumper.
According to the Physics Hypertextbook (http://physics.info/drag/) the typical
skydiver has a terminal velocity of about 55 m/s. This is the velocity needed to
find the force of the impact. But just to make sure I used the Drag Force formula of
Vt=√(2mg/CρA). because I wasn’t sure if this was the same for base jumpers.
For cross sectional area I assumed he was falling on his back/stomach because this
is where most of his injuries occurred so I decided to use a rectangular shape to
determine the cross sectional area of .51 m^2.

Vt=√(2mg/CρA).
Vt=√((2*83.8kg*9.8m/s/s)/(1.0*1.29kg/m^3*.51))
Vt=50. m/s

Using this formula I found a terminal velocity closer to 50m/s. I then could affirm
this velocity by using energy principles (∆KE=-∆PE) to solve for final velocity before
impact.
Vf=√(2gh)
Vf =√(2*9.8 m/s^2*120 m)
Vf=50. m/s.

To find the force with which the man hits the ground, use the equation F= ∆P/∆t
F=0-(83.8kg)(50m/s)/.3s
F=1.4*10^4 N

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