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Grade 11 · unit review

Review: Energy use over time and useful service

Integrate changing power records, account for outputs, and compare energy for a stated task.

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Bring the unit skills together

Use these 4 new cases to check your reasoning. Choices are temporary and are not saved to an account, sent to staff or recorded as school grades. Download your current review choices before leaving or reloading.

Unit review questions
1. A constant 75 W model operates for 2.5 h. What energy is used?
2. A device uses 25 W for 6 h and 2 W for 18 h in a day. What total energy does the piecewise model give?
3. A device receives 800 J, transfers 200 J as useful output and 560 J thermally, with no other transfers. Which pair fits?
4. A service needs score at least 700 for 3 h. A: 20 W, score 720; B: 16 W, score 710; C: 10 W, score 650. Which qualifies with least energy?

The download contains your current choices and any checked feedback. Keep the separate transfer-task work in your own document; downloading its instructions does not mark it complete.

Use the skills in a new task

Prepare a paper recommendation for a fictional information display needing light score at least 600 for 5 active hours daily. X has score 640, uses 18 W active and 2 W for the other 19 h; Y has score 610, uses 16 W active and 3 W for 19 h; Z has score 550, uses 10 W active and 1 W for 19 h. Assume constant power per interval. Compare daily energy and qualification. In a separate X output interval, input is 200 J, light 60 J, thermal output 130 J; account for the rest and calculate light efficiency.

Work on paper or in your own document. Explain the choices you made.

  • Check all 24 hours for each energy total.
  • Calculate X 128 Wh, Y 137 Wh, Z 69 Wh and convert qualifying totals to kWh.
  • Choose X among qualifying plans; exclude Z by light score.
  • Find a 10 J storage increase and 30% light efficiency for the separate X interval.
Compare with a model response

X uses 18×5 + 2×19 = 128 Wh = 0.128 kWh daily. Y uses 16×5 + 3×19 = 137 Wh = 0.137 kWh. Z uses 69 Wh but fails the 600-score requirement. X and Y qualify, so X minimizes the supplied daily energy despite having higher active watts. In the separate X ledger, 200 − 60 − 130 = 10 J increase stored energy; light efficiency is 60/200 = 30%.

A different response can also meet the criteria. Compare the evidence and reasoning, rather than copying the wording.