(i)

The law of conservation of energy states that energy cannot be created nor destroyed but can be transformed from one form into another.

(ii)

Just before it touches the ground, potential energy equals kinetic energy.

Potential energy = mass x acceleration due to gravity x height

Kinetic energy = $\frac{1}{2}$ x mass x velocity²

Mass = 25 kg

Acceleration due to gravity = 10 ms^-2

Height = 10 m

25 x 10 x 10 = $\frac{1}{2}$ x 25 x velocity²

Get rid of the fraction by multiplying both sides by the denominator 2

2 x 25 x 10 x 10 = 2 x $\frac{1}{2}$ x 25 x velocity²

2 x 25 x 10 x 10 = 1 x 25 x x velocity²

Divide both sides by 25

velocity² = $\frac{\mathrm{2\; x\; 25\; x\; 10\; x\; 10}}{25}$

velocity² = 200

Take the square root of both sides.

velocity = $\sqrt{\mathrm{200}}$ = 14.1421356237 ms^-1 ≈ 14.14 ms^-1

(i)

The principle of conservation of energy states that energy is neither created nor destroyed but can be changed/transferred/transformed from one form to another

OR

The principle of conservation of energy states that in a closed system, the total energy is constant.

(ii)

Energy transformation in

(i)

Three other sources of electric power generation

1. Nuclear
2. Solar
3. Wind

(ii)

Energy transformation in any two

Solar → sunlight → electrical
Wind → mechanical → electrical