O Levels Physics (5054)•5054/11/M/J/21
Explanation
Calculate total energy consumption in kWh and multiply by cost per unit
Steps:
- Total days: 3 weeks × 7 days/week = 21 days.
- Total hours: 21 days × 5 hours/day = 105 hours.
- Energy used: 100 W = 0.1 kW; 0.1 kW × 105 hours = 10.5 kWh.
- Total cost: 10.5 kWh × 2.52.
Why C is correct:
- Energy cost formula: total kWh = power (kW) × time (h), then cost = kWh × rate per kWh, yielding exactly $2.52.
Why the others are wrong:
- A: Underestimates time, perhaps only 5 hours total (0.1 kW × 5 h × 0.12, but doubled incorrectly).
- B: Uses 1 week only (0.1 kW × 35 h × 0.84).
- D: Assumes 20 days (0.1 kW × 100 h × 2.40, close but wrong).
Final answer: C
Topic: Uses of electricity
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