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 sources are increasingly utilized for electricity supply due to their sustainability and lower environmental impact compared to non-renewable sources. They help reduce greenhouse gas emissions and dependence on finite resources, aligning with global efforts to combat climate change.

To find the minimum height, we use the formula for gravitational potential energy:

$ext{(PE)} = mgh$

Where:

• $PE$ = potential energy (which is equal to the kinetic energy gained, 1300 J)
• $m$ = mass (7.0 kg)
• $g$ = acceleration due to gravity (approximately 10 m/s²)
• $h$ = height in meters

Rearranging the formula for height: $h = \frac{PE}{mg} = \frac{1300}{7.0 \times 10} = 18.57 ext{ m}$ Thus, the minimum height water must fall is approximately 18.57 meters.

Using the formula for kinetic energy:

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

Where:

• $KE$ = kinetic energy (1100 J)
• $m$ = mass of moving water (8.0 kg)
• $v$ = velocity (speed)

Rearranging for speed, we have: $v = \sqrt{\frac{2KE}{m}} = \sqrt{\frac{2 \times 1100}{8.0}} = \sqrt{275} \approx 16.58 ext{ m/s}$ Thus, the speed of the moving water as it enters the turbine is approximately 16.58 m/s.

To find the percentage of kinetic energy transferred to the turbine, we need to determine the kinetic energies before and after the turbine:

• Before turbine: 15 m/s roughly corresponds to 7.5 kJ (from the graph).
• After turbine: 13 m/s corresponds to about 5.0 kJ.

Now, the kinetic energy transferred is: $KE_{transferred} = KE_{initial} - KE_{final} = 7.5 - 5.0 = 2.5 ext{ kJ}$

The percentage transferred can be calculated as: $Percentage = \left(\frac{KE_{transferred}}{KE_{initial}}\right) \times 100 = \left(\frac{2.5}{7.5}\right) \times 100 \approx 33\%$ Thus, about 33% of the kinetic energy is transferred to the turbine.