7(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 - Question 7 - 2018 - Paper 1

Renewable energy sources such as wind, solar, and hydroelectric power are increasingly adopted because they are sustainable and help reduce greenhouse gas emissions. As technology advances, the efficiency and affordability of renewable energy systems improve, making them more attractive options for countries looking to meet energy demands while minimizing environmental impact.

To calculate the minimum height, we can use the formula for gravitational potential energy: $ext{Potential energy (PE)} = mgh$ Where: m = mass of water = 7.0 kg, g = acceleration due to gravity = 10 m/s², h = height in meters.

Rearranging the formula to solve for height (h): $h = \frac{PE}{mg}$ Now substituting the given values: $h = \frac{1300}{7.0 \times 10} = \frac{1300}{70} \approx 18.57 ext{ m}$ Thus, the minimum height is approximately 18.57 meters.

To find the speed of the moving water, we can use the kinetic energy formula: $KE = \frac{1}{2} mv^2$ Where: KE = kinetic energy = 1100 J, m = mass = 8.0 kg, v = speed in m/s.

Rearranging the formula gives us: v = \sqrt{\frac{2 \cdot KE}{m}} = \sqrt{\frac{2 \cdot 1100}{8.0}} = \sqrt{275} \approx 16.58 ext{ m/s}. Therefore, the speed of the moving water as it enters the turbine is approximately 16.58 m/s.

From the graph, we can observe the kinetic energy at 15 m/s, which is approximately 8 kJ, and at 13 m/s, which is about 6 kJ. The energy transferred to the turbine is:

$\text{Energy transferred} = \text{Initial energy} - \text{Final energy} = 8 \text{ kJ} - 6 \text{ kJ} = 2 \text{ kJ}$

To find the percentage of kinetic energy transferred:

$\text{Percentage} = \left( \frac{\text{Energy transferred}}{\text{Initial energy}} \right) \times 100 = \left( \frac{2 \text{ kJ}}{8 \text{ kJ}} \right) \times 100 = 25\%$

Thus, the percentage of kinetic energy transferred from the air is 25%.