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S4 Physics: Heat Capacity and Heat Transfer Paper 3 (finding mass, mixing and measuring c)
S4 Physics: Heat Capacity and Heat Transfer Paper 3 (finding mass, mixing and measuring c)
Paper 3 asks everything backwards: mass or rise from energy, then a mixing experiment to measure an unknown c.
Quick answer 2 kg; 9,000 J; 100 C; a good conductor such as a metal; 50 C; 30 C; B warms half as much as A; 560 J per kg per degree; 400 s; a high temperature does not mean a large heat capacity.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | 25 minutes |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S4 Physics: Heat Capacity and Heat Transfer |
| Level | S4 |
02 Questions (10 items)
- FoundationThe water in a container has a heat capacity of 8,400 J per degree at 4,200 J per kg per degree. Find its mass.
- Foundation0.4 kg of iron is heated from 15 C to 65 C at 450 J per kg per degree. Find the energy absorbed.
- FoundationThree kilograms of water absorbs 1.26 MJ. By how much does its temperature rise?
- FoundationWhat do we call a material that carries heat away quickly, and name one example.
- IntermediateHalf a kilogram of water at 90 C is mixed with half a kilogram at 10 C. Find the final temperature.
- Intermediate0.2 kg of water at 90 C is added to 0.6 kg at 10 C. Find the final temperature to one decimal place.
- IntermediateTwo identical heaters warm A (1 kg of water) and B (2 kg). After the same time, how do the rises compare?
- Challenge0.25 kg of metal at 100 C is dropped into 0.5 kg of water at 20 C and the final temperature is 25 C. Find the specific heat capacity of the metal, taking water as 4,200 J per kg per degree.
- ChallengeA 1.5 kW heater raises 2 kg of water from 25 C to 75 C at 70 per cent efficiency. How many seconds does it need?
- Error redoA student believes that the hotter an object is, the larger its heat capacity. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 2 kg | Since C equals m times c, mass is 8,400 over 4,200, or 2 kg. |
| 2 | 9,000 J | The rise is 50 degrees, so 0.4 times 450 times 50 gives 9,000 J. |
| 3 | 100 C | 1,260,000 divided by 12,600 gives 100 degrees. |
| 4 | A good conductor, for example a metal such as copper or aluminium | Good conductors have many free electrons; poor ones such as wood or plastic make good handles. |
| 5 | 50 C | With equal masses the final temperature is the simple average, 50 C. |
| 6 | 30 C | The weighted average is (18 + 6) over 0.8, which gives 30 C. |
| 7 | B warms half as much as A | For equal energy the rise is E over mc, so doubling the mass halves the rise. |
| 8 | 560 J per kg per degree | The water gains 10,500 J; the metal falls 75 degrees, so c is 10,500 over 18.75, or 560. |
| 9 | 400 s | The water needs 420,000 J, the supply must be 600,000 J, and at 1,500 W that is 400 s. |
| 10 | Heat capacity depends only on mass and material, not on temperature. | Temperature is a state while heat capacity is a property; the same jug has the same value at any temperature. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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