IGCSE · 1 · structured
Motion, forces and energy · Question 9
Motion, forces and energy · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- routine
- Marks
- 8
- Topics
- 2
- Answer
- Complete
A wind turbine generates electricity for a school. Over a period of 60 s, the moving air delivers 900 kJ of energy to the turbine blades. The electrical output of the turbine during this time is 9.0 kW.
- (a)
State State two renewable energy resources other than wind.
2 marks - (b)
Calculate Calculate the input power delivered to the blades by the moving air.
2 marks - (c)
Calculate Calculate the efficiency of the turbine.
2 marks - (d)
Explain Explain why the efficiency of the turbine can never reach 100%.
2 marks
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(a)
State State two renewable energy resources other than wind.
Answer the command word directly and use precise physical vocabulary. Include only the distinct features or facts that earn marks, without burying them in unrelated background information.
- 1
any one of: solar / hydroelectric / tidal / wave / geothermal / biofuel
- 2
a second, different one from the same list
(b)
Calculate Calculate the input power delivered to the blades by the moving air.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
P = E / t = 900 000 / 60
- 2
P = 15 000 W = 15 kW
(c)
Calculate Calculate the efficiency of the turbine.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
efficiency = useful output power / total input power = 9.0 / 15
- 2
= 0.60 or 60%
(d)
Explain Explain why the efficiency of the turbine can never reach 100%.
State the outcome first, then link cause to effect with the relevant physical principle. Each link in the reasoning should be explicit enough to earn its own marking point.
- 1
some energy is always transferred to non-useful stores — friction in the bearings and gearbox heats the surroundings, and sound is emitted
- 2
and the air must still be moving after it passes the blades, so it keeps some kinetic energy
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