Understanding the Concepts

* Free Fall: The rock is in free fall, meaning the only force acting on it is gravity.

* Acceleration due to Gravity: The acceleration due to gravity (g) is approximately 9.8 m/s². This means the rock's speed increases by 9.8 meters per second every second it falls.

* Kinematic Equations: We can use the following kinematic equation to find the final velocity (v):

v² = u² + 2as

where:

* v = final velocity (what we want to find)

* u = initial velocity (0 m/s since the rock is dropped)

* a = acceleration due to gravity (9.8 m/s²)

* s = distance (15 m)

Calculations

1. Plug in the values:

v² = 0² + 2 * 9.8 * 15

2. Simplify:

v² = 294

3. Solve for v:

v = √294 ≈ 17.15 m/s

Answer: The rock will be moving at approximately 17.15 meters per second just before it strikes the ground.