Find time when position less than zero

I have code that integrates velocity to get position. I want to know when the position of projectile = 0 (ie time of flight), but there is no value in position vector where position = 0 at time of flight as position is measured periodically.

i.e How can I calculate time of flat for a projectile (intercept of position=0) when height of projectile is measured periodically?

This is the code I have to calculate position:

for t = 1:1:1500
v = cumtrapz(time,acceleration)
position = cumtrapz(time,v)

if t <= (60/dt)
        acceleration(t) =  (Fup-Fdown) /mass
    else       
        acceleration(t) =  (-Fdown) /mass;
    end
time(t) = t*dt; 
end

[Jan]

@afrhy: It is impolite to delete the question after someone has spent the time to post an answer. Please stop this. When you participate in the forum, the terms of use involve, that you are willing to share your questions with the community.

Answer 1

[Star Strider]

I cannot run your code.

You can get the index of the first position that is negative using the find function:

negpos - find(position <= 0, '1, 'first');

The time will then be either:

tfinal = t(negpos)

or

tfinal = time(negpos)

depending on what you want.