Conservation of Energy

Since the ball starts from rest at height $h$, all energy is initially GPE. At the bottom, all energy is KE. We use: $mgh=\frac{1}{2}m{v}^2$

The mass $m$ appears on both sides, so it cancels: $gh=\frac{1}{2}{v}^2$

Substituting $g=10{\text{m/s}}^2$ and $h=5\text{m}$: $10\times 5=\frac{1}{2}{v}^2$ $50=\frac{1}{2}{v}^2$ $v^2=100$

Taking the square root: $v=\sqrt{100}=10\text{m/s}$. Notice the mass of the ball (4 kg) was not needed — all objects fall at the same speed regardless of mass in ideal conditions.

We need the speed at the bottom of a 5 m fall. Using $mgh=\frac{1}{2}m{v}^2$, we get $v=\sqrt{2gh}=\sqrt{2\times 10\times 5}=\sqrt{100}$.

If $v=5\text{m/s}$, then $KE=\frac{1}{2}(4)(25)=50\text{J}$, but $GPE=4\times 10\times 5=200\text{J}$. These are not equal, so 5 m/s is incorrect.

If $v=20\text{m/s}$, then $KE=\frac{1}{2}(4)(400)=800\text{J}\ne 200\text{J}$. If $v=50\text{m/s}$, $KE$ would be enormous — far more than the available GPE. Both are eliminated.

With $v=10\text{m/s}$: $KE=\frac{1}{2}(4)(100)=200\text{J}$ and $GPE=4\times 10\times 5=200\text{J}$. These match, confirming 10 m/s is correct.

At the highest point, the pendulum is momentarily at rest, so $KE=0$ and all energy is stored as GPE. At the lowest point, height is zero (reference level), so $GPE=0$ and all energy is KE.

As the pendulum descends, height decreases so GPE decreases. Speed increases so KE increases. The transformation is: GPE → KE.

The correct description is that gravitational potential energy converts to kinetic energy as the pendulum swings from its highest to its lowest point.

The pendulum moves downward from high point to low point, so height decreases and speed increases.

"Kinetic energy converts to gravitational potential energy" describes the upward swing (low to high), not the downward swing. This is the reverse of what is asked.

"Thermal energy converts to kinetic energy" is incorrect — thermal energy is a product of friction, not a starting source for the pendulum's motion. Energy does not spontaneously convert from thermal to kinetic in this scenario.

"Gravitational potential energy is destroyed" violates the Law of Conservation of Energy, which states energy cannot be created or destroyed. This option is fundamentally wrong.

The only correct option is "Gravitational potential energy converts to kinetic energy", which accurately describes the downward swing of a pendulum.