In this problem, a ferry moves with increasing speed (it returns back so the velocity is negative) from velocity $v_text{i} = 0$ to $v_text{f} = -5.8~mathrm{m/s}$ in time interval $Delta t = 9.25~mathrm{s}$. We find its average acceleration.

The average acceleration is

$$
begin{align*}
a_text{av} &= frac{Delta v}{Delta t} \
&= frac{-5.8~mathrm{m/s} – 0}{9.25~mathrm{s}} \
&= -0.62703~mathrm{m/s^{2}} \
a_text{av} &= boxed{ -0.63~mathrm{m/s^{2}} }
end{align*}
$$

$$
a_text{av} = -0.63~mathrm{m/s^{2}}
$$

In this problem, we are given that a car with initial speed $v_text{i} = 22~mathrm{m/s}$ decelerates to rest at rate $a_text{av} = -6.1~mathrm{m/s^{2}}$. We find the time it take for the car to rest.

The equation we need to use is

$$
begin{align*}
Delta t &= frac{Delta v}{a_text{av}} \
&= frac{0 – 22~mathrm{m/s}}{-6.1~mathrm{m/s^{2}}} \
&= 3.60656~mathrm{s} \
Delta t &= boxed{ 3.6~mathrm{s} }
end{align*}
$$

$$
Delta t = 3.6~mathrm{s}
$$

In this problem, a rock is dropped on the Moon. The acceleration on the surface is $a_text{av} = 1.62~mathrm{m/s^{2}}$ and it takes some time $Delta t = 2.4~mathrm{s}$. We find the speed of the rock as it hits the surface.

The rock starts from rest, hence

$$
begin{align*}
v_text{f} &= v_text{i} + a_text{av}Delta t \
&= 0 + left( 1.62~mathrm{m/s^{2}} right) left( 2.4~mathrm{s} right) \
&= 3.888~mathrm{m/s} \
v &= boxed{ 3.9~mathrm{m/s} }
end{align*}
$$

$$
v_text{f} = 3.9~mathrm{m/s}
$$