# How do I model the falling of a skydiver using a DF?

1. Oct 14, 2009

### thename1000

• I'm given the initial conditions vnot=0m/s, hnot=3000m, and tnot=0s

After 35 seconds of freefall, the chute opens.

I am to write a piece-wise define diff equation for the rate of change of velocity, with the two pieces t<35 and t >_35.

I am not given a mass.

Now, I understand how to start at http://media.wiley.com/Lux/97/19597.nce030.jpg

And how to go to http://media.wiley.com/Lux/00/19600.nce033.jpg. (where b=k/m)

This represents the sky diver initially falling without a parachute.

And this with a chute: http://media.wiley.com/Lux/03/19603.nce036.jpg

Three questions:

1.) Since I'm not given a mass, and are supposed to graph both solutions, how do I do this?

2.) Do I use the initial height anywhere in this equation?

3.) Once I solve each equation, what do I do with the piecewise part numbers? ( t<35 and t >_35.)

Thanks for any help

Last edited by a moderator: Apr 24, 2017
2. Oct 14, 2009

### g_edgar

Just write m in your derivations for the mass. And marvellously, m cancels out. Legend says that Galilleo dropped two different weights from a tower to demonstrate this fact that the mass doesn't matter...