Help on User Defined Function

[xc405]

I have created a function that calculates a final velocity of a skydiver:

Function David(vi, g, c, m, tf, ti, dt)
    n = (tf - ti) / dt
    v = vi
    t = ti
For i = 1 To n
    v = v + (g - (c / m) * v) * dt
Next i
    David = v
End Function

Now i want the function to automatically use c=50 once t=10 seconds.
Does anyone know?

 

[Ralajer]

This is your function adding a time increment and if statement to change c when t >= 10 secs

Function David(vi, g, c, m, tf, ti, dt)
    n = (tf - ti) / dt
    v = vi
    t = ti
For i = 1 To n
    If t >= 10 Then c = 50
    v = v + (g - (c / m) * v) * dt
    t = t + dt
Next i
    David = v
End Function

 

[xc405]

It doesn't work, it gives me an answer of 20 and it should be much higher. I took away the time step and I got 15.68 so I'm
Not sure if it's working right. Thanks for the help though.

 

[Ralajer]

I didn't check the physics of your problem I just provided the code required to change c at time = 10. It been a while since my first semester of physics where we covered this sort of problem so could you link to or otherwise reference the equation you are using. There is also the question of terminal velocity.

The input used in the function and the expected result would also helpful. Saying it's returning 20 doesn't mean much I don't even know what units you are using.