Respuesta :

We are told the given equation:

[tex]y(t) = 0.2 + 8t - 10t^2[/tex]

When a particle is not moving, the velocity is zero. Thus we have to find the first derivative.

[tex]y'(t) = v(t) = 8-20t[/tex]

Now set v(t) = 0, and we get

[tex]8-20t = 0 [/tex]

8 = 20t

t = 8/20 s

Hope this helps
AL2006
The speed of the particle is zero when t is 0.4 second. But it's only at that instant. There's no time "interval".