Question

Is there any time interval during which the particle is not moving?

Answer 1

We are told the given equation:

$y(t) = 0.2 + 8t - 10t^2$

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

$y'(t) = v(t) = 8-20t$

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

$8-20t = 0$

8 = 20t

t = 8/20 s

Hope this helps

Answer 2

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".