What happens to the PE if the stone falls to the ground

Step 1: Gravitational potential energy (PE) is defined as
$PE = m g h$
where $m$ is mass in kg, $g \approx 9.8$ m/s² is acceleration due to gravity, and $h$ is height above the ground in m. Units of PE are joules (J).

Step 2: Before falling, assume the stone is at height $h$ above ground.
Initial PE:
$PE_i = m g h \quad (J)$

Step 3: When the stone falls to the ground, $h = 0$ m.
Final PE:
$PE_f = m g \times 0 = 0 \quad J$

Step 4: Change in PE:
$\Delta PE = PE_f - PE_i = 0 - m g h = -m g h \quad J$

The PE decreases to 0 J (taking ground level as the zero reference point).
The PE becomes 0 J