Simple harmonic motion help pls

SO I have stuck by the following question, can anyone help to explain?
Its question b thanks

I cannot seem to see any question.

I’ve inserted the pic below, thanks!

I’ve inserted the pic below, thanks!

here is the question.

Frequency of oscillation = 2pi/4.5 =4pi/9
Amplitude of oscillation = 1.15 m
x = 1.15 cos 4pi t /9
0.6 m means the amplitude is -0.55m

0.55 = 1.15 cos 1.4 t
t = 0.766 s

so time = 4.5 - 2 x 0.766 = 3.0 s

…0.6 m means the amplitude is -0.55m ....

Frequency of oscillation = 2pi/4.5 =4pi/9
Amplitude of oscillation = 1.15 m
x = 1.15 cos 4pi t /9
0.6 m means the amplitude is -0.55m

0.55 = 1.15 cos 1.4 t
t = 0.766 s

so time = 4.5 - 2 x 0.766 = 3.0 s

Try to model the SHM motion using a trigonometric function such as -Acos(ωt), where the barrier starts from the bottom. The height of the barrier moves is 2A.

Assume that the barrier starts at the bottom or -A, the barrier first reaches (-A + 0.60 m) at time t₁ and then at time t₂. The time difference between t₁ and t₂ will be the maximum time.

I don’t really understand ‘
Assume that the barrier starts at the bottom or -A, the barrier first reaches (-A + 0.60 m) at time t₁ and then at time t₂. The time difference between t₁ and t₂ will be the maximum time’ can you explain a bit more?many thanks!!!

If you look at the picture, the black line represents the ground. When I say “Assume that the barrier starts at the bottom or -A,” meaning the bottom of the barrier starts its motion from the ground. (I know the description is bad in the previous post. )

The pink line in the picture shows the position of (-A + 0.60 m) from the ground while the red curve is modelling the motion of the bottom of the barrier. When the bottom of the barrier reaches the position (-A + 0.60 m) for the first time is around 0.7 s and the second time is around 3.7 s as shown by the intersection between the pink line and red curve. The difference between the 2 timings would be the maximum time.

If you look at the picture, the black line represents the ground. When I say “Assume that the barrier starts at the bottom or -A,” meaning the bottom of the barrier starts its motion from the ground. (I know the description is bad in the previous post. )

The pink line in the picture shows the position of (-A + 0.60 m) from the ground while the red curve is modelling the motion of the bottom of the barrier. When the bottom of the barrier reaches the position (-A + 0.60 m) for the first time is around 0.7 s and the second time is around 3.7 s as shown by the intersection between the pink line and red curve. The difference between the 2 timings would be the maximum time.

But I don’t understand why it would reach the position(-A+0.6)?

I am not sure how can explain this. The question states that "A contestant requires a space at least 0.6 m high to get under the barrier." So the barrier need to moves up by 0.6 m.

If you are at basement level 5, which i called -5, when you move up 3 levels, isn't -5 + 3.