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 sources, such as solar and wind, are becoming more popular due to several reasons:

1. Sustainability: Unlike fossil fuels, renewable sources are sustainable and can be replenished naturally, ensuring a continuous supply of energy.

2. Environmental Benefits: The use of renewables reduces greenhouse gas emissions and minimizes the impact on the environment, making them a preferred choice for meeting climate goals.

3. Technological Advances: Improvements in technology have made renewable energy systems more efficient and cost-effective, leading to greater adoption.

4. Government Policies: Many countries offer incentives and subsidies for renewable energy, encouraging investment in this sector.

To calculate the minimum height, we use the formula for gravitational potential energy (GPE), which is equal to the kinetic energy (KE) when the water falls:

$GPE = mgh$

Where:

• $m$ = mass (7.0 kg)
• $g$ = acceleration due to gravity (approximately $9.81 ext{ m/s}^2$)
• $h$ = height

Setting GPE equal to KE gives:

$1300 J = 7.0 kg imes 9.81 ext{ m/s}^2 imes h$

Rearranging gives:

$h = \frac{1300 J}{7.0 kg imes 9.81 ext{ m/s}^2}$

Calculating this gives:

$h \approx 18.3 m$

Thus, the minimum height is approximately 18.3 m.

We can find the speed of the moving water using the kinetic energy formula:

$KE = \frac{1}{2} mv^2$

Where:

• $KE = 1100 J$
• $m = 8.0 kg$
• $v$ is the speed

Rearranging for $v$:

$v = \sqrt{\frac{2 \cdot KE}{m}} = \sqrt{\frac{2 \cdot 1100 J}{8.0 kg}}$

Evaluating gives:

$v \approx 17 m/s$

Thus, the speed of the moving water as it enters the turbine is approximately 17 m/s.

From the graph, we can read the kinetic energy values:

• For wind speed of 15 m/s, kinetic energy is roughly 5.2 kJ.
• For wind speed of 13 m/s, kinetic energy is roughly 3.9 kJ.

The kinetic energy transferred to the turbine can be calculated as:

$\text{Energy Transferred} = 5.2 kJ - 3.9 kJ = 1.3 kJ$

To find the percentage of kinetic energy transferred to the turbine:

$\text{Percentage} = \left(\frac{1.3 kJ}{5.2 kJ}\right) \times 100 = 25 \%$

Therefore, the percentage of kinetic energy transferred from the air to the turbine is 25%.