Distinguish between hay and silage, list 3 protein sources for poultry, and calculate energy and velocity of a falling body.

Mass $m = 10 \text{ kg}$
Initial height $h_1 = 20 \text{ m}$
Final height $h_2 = 5 \text{ m}$
Initial velocity $v_1 = 0 \text{ m/s}$ (since it was placed)
Acceleration due to gravity $g = 9.8 \text{ m/s}^2$

The total mechanical energy at the initial height equals the total mechanical energy at the final height.

Since $v_1 = 0$, the initial kinetic energy is zero.

Divide by $m$:

Rearrange to find $v_2^2$:

The velocity of the body at height $5 \text{ m}$ above the ground is $\boxed{\text{17.15 m/s}}$.

2(c)(i) State three benefits that humans derive from the nitrogen cycle.

• It provides nitrogen for the synthesis of proteins and nucleic acids (DNA, RNA), which are essential for all life.
• It enriches soil fertility through the formation of nitrates, supporting agricultural productivity.
• It enables the production of industrial chemicals like ammonia, used in fertilizers and explosives.

2(c)(ii) State two human activities that affect the nitrogen cycle.

• The extensive use of synthetic nitrogen fertilizers in agriculture.
• The burning of fossil fuels, which releases nitrogen oxides into the atmosphere.

2(d)(i) A colourless liquid in the laboratory was suspected to be water. Describe briefly a test to confirm that the liquid is water.
Add a few drops of the liquid to anhydrous copper(II) sulfate. If the white powder turns blue, the liquid is confirmed to be water.

2(d)(ii) State two stages in the large-scale water treatment.

• Filtration: Water passes through layers of sand and gravel to remove smaller suspended particles.
• Disinfection: Chemicals like chlorine are added to kill harmful microorganisms.

3(a) The nuclides of sodium and fluorine are represented as $^{23}_{11}\text{Na}$ and $^{19}_{9}\text{F}$ respectively.
(I) Protons in each atom.

• For $^{23}_{11}\text{Na}$: The atomic number (subscript) is 11, so it has 11 protons.
• For $^{19