5. (a) Which of these is a non-renewable source of energy? A geothermal B natural gas C tidal D solar (b) Explain why renewable sources provide an increasing fraction of the electricity supply for many countries - Edexcel - GCSE Physics Combined Science - Question 5 - 2018 - Paper 1

Renewable energy sources, such as solar, wind, and hydro, are becoming increasingly vital for many countries due to their sustainability and minimal environmental impact. Unlike fossil fuels, which are finite and contribute to environmental degradation, renewable sources are abundant and have lower carbon footprints. Government policies and technological advancements have made it more feasible to harness these resources, leading to their growing share in electricity generation. Additionally, as the cost of renewable technologies declines, investment in these energy sources further increases their contribution to the electricity supply.

To find the minimum height, we use the formula for gravitational potential energy:
$PE = mgh$
where:

• $PE$ is the potential energy (equal to kinetic energy gained, which is 1300 J),
• $m$ is the mass of the water (7.0 kg),
• $g$ is the acceleration due to gravity (approximately 9.81 m/s²),
• $h$ is the height (unknown).

Rearranging the formula gives us:
$h = \frac{PE}{mg}$
Substituting the values:
$h = \frac{1300}{7.0 \times 9.81} \approx 18.3 m$
Thus, the minimum height is approximately 18.3 m.

To calculate the speed, we can use the kinetic energy formula:
$KE = \frac{1}{2}mv^2$
Rearranging gives us:
$v = \sqrt{\frac{2 \times KE}{m}}$
Substituting the values:
$v = \sqrt{\frac{2 \times 1100}{8.0}} \approx 17 ext{ m/s}$
Hence, the speed of the moving water as it enters the turbine is approximately 17 m/s.

From the graph, we determine the kinetic energy before and after passing through the turbine.
At a wind speed of 15 m/s, the kinetic energy is approximately 5.2 kJ, and at 13 m/s, it is around 3.9 kJ.
To find the percentage of kinetic energy transferred:

1. Calculate the kinetic energy lost:
   $\Delta KE = 5.2 - 3.9 = 1.3 \ ext{ kJ}$
2. Calculate the percentage transferred:
   $\text{Percentage} = \left(\frac{\Delta KE}{KE_{initial}}\times 100\right) = \left(\frac{1.3}{5.2} \times 100\right) \approx 25 \%$
   Thus, approximately 25% of the kinetic energy is transferred to the turbine.