Hydroelectricity is the best answer.
This is an article by the EIA, but the pie graph is the most helpful: https://www.eia.gov/energyexplained/?page=us_energy_home
Answer:
Explanation:
Given
mass of ice 
Height of hill 
Neglecting air resistance
As resistance is absent so Energy at top of hill and at the bottom hill is conserved.
Energy at top is equal to Potential Energy

Energy at bottom is equal to kinetic energy at bottom




Most of the question 1 is chopped off so I'll try my best to answer.
1ai) In a telephone, the sound is converted into electrical signals before being sent through the wire before converted back into sound.
1aii) Sound travels by the collision between particles. In solids, the particles are closely packed (as compared to air molecules) and thus collide with their neighbors quickly after being disturbed, allowing for sound to be passed on at a faster rate.
b) Can't help much on this one.
Answer:

Explanation:
When the screw is turned by two turns then change in the length of the wire is given as




now we know by the formula of Young's modulus

so we have


