V₃ = 1.2\,A x 2

As the North pole of the magnet moves into the solenoid, an induced current will flow to create a magnetic field that opposes this motion. To oppose the incoming North pole, end X of the solenoid must become a North pole.
The polarity of end X of the solenoid is $\boxed{\text{North pole}}$.

8. (b)

i)
Points $\boxed{\text{A and D}}$ are in phase.
Explanation: Both points A and D represent crests of the wave, meaning they have the same maximum positive displacement and are at the same stage of their oscillation.

ii)
The distance from $\boxed{\text{A to D}}$ represents one wavelength.
Explanation: This distance covers one complete cycle of the wave, from one crest to the next consecutive crest.

iii)

Wavelength, $\lambda = 0.8\,\text{m}$
Speed, $v = 20\,\text{m/s}$

The relationship between speed, frequency, and wavelength is $v = f \lambda$.
Rearrange to solve for frequency: $f = \frac{v}{\lambda}$.

The frequency of the wave is $\boxed{\text{25 Hz}}$.

iv)

• Wave pulse: A single, non-repeating disturbance or short burst of energy that travels through a medium.
• Wave train: A continuous series of periodic waves that propagates through a medium, consisting of multiple wave cycles.

8. (c)

• Promoting the use of renewable energy sources: Shifting from fossil fuels to sources like solar, wind, and hydroelectric power reduces air pollution and greenhouse gas emissions.
• Implementing stricter regulations on industrial emissions and waste disposal: This ensures that factories and industries release fewer pollutants into the air and water, and manage their waste responsibly.