The Physics Question Bank

Course: Combined Science + Separate Physics  |  Tier: Foundation + Higher  |  Equation sheet: given in the exam

The equation

energy for a change of state = mass × specific latent heat    E = m L

Quantity	Symbol	Unit
energy	E	joules (J)
mass	m	kilograms (kg)
specific latent heat	L	joules per kilogram (J/kg)

Rearranged: m = E ÷ L  |  L = E ÷ m  |  Ice melting (fusion): L = 334 000 J/kg; water boiling (vaporisation): L = 2 260 000 J/kg. The temperature does not change during a change of state.

Use FIFA for every answer

• F – Formula: write the equation as it appears on the sheet.
• I – Insert: put in the numbers (convert to standard units first).
• F – Fix: rearrange to make the unknown the subject.
• A – Answer: calculate and always give the unit.

Foundation: aim for Q1–8.   Higher: aim for Q4–10. Most questions need rearranging.

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Questions

Q1 (F) How much energy is needed to melt 2 kg of ice at 0 °C? (L = 334 000 J/kg)

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F: E = m L
I: E = 2 × 334 000
F: E is already the subject
A: 668 000 J

Q2 (F) 1 002 000 J of energy is supplied to ice at 0 °C in a cool box. What mass of ice melts? (L = 334 000 J/kg)

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F: E = m L
I: 1 002 000 = m × 334 000
F: m = 1 002 000 ÷ 334 000
A: 3 kg

Q3 (F) 105 000 J is needed to melt 0.5 kg of candle wax at its melting point. Calculate the specific latent heat of fusion of the wax.

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F: E = m L
I: 105 000 = 0.5 × L
F: L = 105 000 ÷ 0.5
A: 210 000 J/kg

Q4 (F) 16.7 kJ of energy is transferred to ice cubes at 0 °C in a drink. What mass of ice melts, in grams? (L = 334 000 J/kg)

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Convert first: 16.7 kJ = 16 700 J
F: E = m L
I: 16 700 = m × 334 000
F: m = 16 700 ÷ 334 000 = 0.05 kg
A: 50 g

Q5 (F) A kettle of boiling water is supplied with 452 kJ. What mass of water turns to steam? (L = 2 260 000 J/kg)

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Convert first: 452 kJ = 452 000 J
F: E = m L
I: 452 000 = m × 2 260 000
F: m = 452 000 ÷ 2 260 000
A: 0.2 kg

Q6 (F/H) 1.26 MJ is needed to boil away 1.5 kg of ethanol at its boiling point. Calculate its specific latent heat of vaporisation in kJ/kg.

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Convert first: 1.26 MJ = 1 260 000 J
F: E = m L
I: 1 260 000 = 1.5 × L
F: L = 1 260 000 ÷ 1.5 = 840 000 J/kg
A: 840 kJ/kg

Q7 (F/H) A 2.0 kW kettle is left boiling for 113 s. What mass of water turns to steam? (L = 2 260 000 J/kg)

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Energy supplied: E = P t = 2000 × 113 = 226 000 J
F: E = m L
I: 226 000 = m × 2 260 000
F: m = 226 000 ÷ 2 260 000
A: 0.1 kg

Q8 (F/H) In one summer day, part of a glacier absorbs 1.67 × 10¹² J at 0 °C. What mass of ice melts? (L = 3.34 × 10⁵ J/kg)

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F: E = m L
I: 1.67 × 10¹² = m × 3.34 × 10⁵
F: m = 1.67 × 10¹² ÷ 3.34 × 10⁵
A: 5.0 × 10⁶ kg

Q9 (H) 0.50 kg of ice at 0 °C is melted and the water is then warmed to 20 °C. Calculate the total energy needed. (L = 334 000 J/kg; c water = 4200 J/kg °C)

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Step 1 – melting
F: E = m L
I: E = 0.50 × 334 000 = 167 000 J
Step 2 – warming
ΔE = m c Δθ = 0.50 × 4200 × 20 = 42 000 J
A: total = 167 000 + 42 000 = 209 000 J

Q10 (H) A 3.0 kW kettle is accidentally left boiling for 4.0 minutes. What mass of water boils away? Give your answer to 2 significant figures. (L = 2 260 000 J/kg)

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Energy supplied: E = P t = 3000 × 240 = 720 000 J
F: E = m L
I: 720 000 = m × 2 260 000
F: m = 720 000 ÷ 2 260 000 = 0.3186 kg
A: 0.32 kg (2 s.f.)