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Work Power and Efficiency — Free MYP4 Physics Practice Questions
1QuestionEfficiency = Useful Output Total Input x 100Concept Practice
2 marks~3 minCriterion A
A motor lifts a 2 kg mass through a height of 1 m. The energy flow diagram below shows the electrical energy supplied to the motor, the gravitational potential energy gained by the mass, and the thermal energy lost as heat.
State the formula for efficiency, identifying each term in the equation with reference to this motor system. [2]
State the formula for efficiency, identifying each term in the equation with reference to this motor system. [2]
Solutions
2QuestionDefinition and Formula for Work DoneAssessment Practice
5 marks~8 minCriterion C
Data
Mass of block: 0.5 kgTotal distance: 2.0 m
Average applied force: 8.0 N
Change in thermal energy of block and surface: 14.0 J
A student pulls a wooden block at constant speed across a rough horizontal surface. A force sensor records the applied force at five positions:
Additional
| Distance (m) | 0.0 | 0.5 | 1.0 | 1.5 | 2.0 |
|---|---|---|---|---|---|
| Force (N) | 8.0 | 8.1 | 7.9 | 8.0 | 8.0 |
Additional
a
Calculate the work done by the applied force over 2.0 m. [2]
b
The student claims all work done against friction converts entirely to thermal energy in the block and surface. Deduce whether the data support this claim. [2]
c
Identify and analyse one source of systematic error and one source of random error in this experiment, explaining how each affects the calculated work or measured thermal energy. [1]
Solutions
3QuestionEfficiency = Useful Output Total Input x 100Assessment Practice
6 marks~9 minCriterion D
A hospital replaces its entire lighting system with LED bulbs. Each LED bulb consumes 10 W of electrical power and delivers 8 W as useful light output.
a
Define energy efficiency and state its formula. Use the data above to calculate the efficiency of one LED bulb. [2]
b
Explain how LED technology achieves higher efficiency than incandescent bulbs, referring to the energy conversion processes involved. [2]
c
Evaluate the societal benefits and limitations of large-scale adoption of LED lighting in public infrastructure such as hospitals. [2]
Solutions
4QuestionEfficiency = Useful Output Total Input x 100Assessment Practice
6 marks~9 minCriterion D
A school is evaluating a rooftop solar panel installation to reduce energy costs. The panels have a stated efficiency of 20%. On a typical school day, the panels receive 50 kWh of solar energy.
a
Calculate the electrical energy output of the panels for that day. [1]
b
Explain why a 20% efficiency rating means the school cannot rely solely on solar panels to meet its energy needs throughout the year, particularly in a region with variable weather. [2]
c
Evaluate the ethical implications of investing in solar panels that convert only 20% of incident solar energy, considering both the environmental costs of manufacturing and disposal and the long-term benefits of clean energy generation. [3]
Solutions
5QuestionEfficiency = Useful Output Total Input x 100Assessment Practice
12 marks~18 minCriterion C
A student uses a pulley system to lift a heavy box. She records the input work (work done pulling the rope) and the output work (work done lifting the box) across five trials. The results are shown on the graph below.
The student claims the pulley system is approximately 80% efficient across all trials.
| Input Work (J) | 100 | 150 | 200 | 250 | 300 |
|---|---|---|---|---|---|
| Output Work (J) | 72 | 118 | 162 | 208 | 240 |
The student claims the pulley system is approximately 80% efficient across all trials.
a
Calculate the efficiency for each of the five trials. [4]
b
Analyse the student's claim that the system is approximately 80% efficient across all trials, using your results from (a). [3]
c
Evaluate whether friction between the rope and pulley wheel or the weight of the rope itself is the more significant source of energy loss in this system. Justify your reasoning. [3]
d
Discuss ONE limitation of using this laboratory setup to determine the true efficiency of the pulley system in a real-world application. [2]
Solutions
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