- Identify the relationship that ties acceleration, initial velocity, final velocity and displacement. That would be v_f^2 = v_i^2 + 2 \times a \times \Delta x .
- Identify the given quantities in the relationship above. We have v_i = -13 m/s , x_i = 23 m , x_f = 18 m . Therefore, \Delta x = -5 m . Identify the acceleration which is acceleration due to gravity a = -10 m/s^2 .
- Plug in the values to get v_f^2 = 13^2 + 2 \times 10 \times 5 = 269 m^2 /s^2
- Solve for |v_f| = 16.4 m/s . Identify the sign which would be negative as the ball is falling downwards. Therefore, v_f = -16.4 m/s .

Therefore, the object will be falling at the rate of 16.4 m/s when it is 18m above the ground.

I found an answer from www.khanacademy.com

Projectile height given time (video) | Khan Academy

We're just talking about when we get to this point right **over** here. So our final
velocity is just 0 **meters per second**. And we're just going to divide that by 2. This
**will** ...

For more information, see Projectile height given time (video) | Khan Academy

I found an answer from en.wikipedia.org

**Kinematics** - Wikipedia

**Kinematics** is a subfield of classical mechanics that describes the **motion** of
points, bodies ... Then, using arguments from geometry, the position, velocity and
**acceleration** of any ... Velocity Time **physics** graph ... of a body, which is used to
derive equations of **motion** using either Newton's second **law** or Lagrange's
equations.

For more information, see **Kinematics** - Wikipedia

I found an answer from en.wikipedia.org

Equations for a **falling** body - Wikipedia

A set of equations describe the resultant trajectories when **objects** move owing to
a constant ... This assumption is reasonable for **objects falling** to **earth over** the
relatively ... During the first 0.05s the ball drops one unit of distance (about **12** mm
), ... of the **Earth**, the acceleration due to gravity g = 9.807 **m**/**s**^{2} (**meters per**
**second** ...

For more information, see Equations for a **falling** body - Wikipedia

I found an answer from www.quora.com

A ball of mass 8 **kg** is dropped from a height of 10 **m**. What is the ...

Once the **object** hit on the **ground**, height is zero, therefore no potential energy at
**ground** level. We **can** rewrite **above** equation. **Initial** PE = Final KE. The mass **m** ...

For more information, see A ball of mass 8 **kg** is dropped from a height of 10 **m**. What is the ...