O Levels Physics (5054)•5054/12/M/J/20
Explanation
Energy for melting equals mass times latent heat Steps:
- Wax starts at melting point, so all 7700 J melts wax without heating.
- Use formula: thermal energy = mass × specific latent heat of fusion.
- Rearrange: mass = thermal energy / specific latent heat = 7700 J / 220 J/g.
- Calculate: 7700 ÷ 220 = 35 g.
Why D is correct:
- 35 g exactly matches mass = energy / latent heat, the definition for latent heat of fusion.
Why the others are wrong:
- A: 0.5 g needs only 110 J (0.5 × 220), underestimates energy.
- B: 1.7 g needs 374 J (1.7 × 220), ignores most energy.
- C: 12 g needs 2640 J (12 × 220), insufficient for full energy.
Final answer: D
Topic: Melting, boiling and evaporation
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