Answer:
At time t = 0.408 sec diver will be at maximum height
Explanation:
We have given equation of the height
![f(t)=-4.9t^2+4t+9](https://img.qammunity.org/2021/formulas/mathematics/high-school/pbjh2xursm3f57opd36tx9exkcm86qa5vi.png)
We know that velocity is the rate of change of distance with respect to time
So
![v=(df(t))/(dt)=(df(-4.9t^2+4t+10))/(dt)=-9.8t+4+0=-9.8t+4](https://img.qammunity.org/2021/formulas/mathematics/high-school/2yngvxqxoexneeifzxts3ajb55o49qnp80.png)
At maximum height velocity will be zero
So
![-9.8t+4=0](https://img.qammunity.org/2021/formulas/mathematics/high-school/qg9o3oefty4icrp3b67vz2qdlgf72y0vkl.png)
t = 0.408 sec
So at time t = 0.408 sec diver will be at maximum height