IGCSE · 1 · practical
Motion, forces and energy · Question 10
Motion, forces and energy · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 9
- Topics
- 2
- Answer
- Complete
A student determines the density of a small irregularly shaped stone. She has an electronic balance, a measuring cylinder, water and a length of thread. The stone fits easily inside the measuring cylinder.
| Quantity | Reading |
|---|---|
| mass of stone m | 47.6 g |
| volume of water alone V₁ | 50.0 cm³ |
| volume of water and stone V₂ | 68.0 cm³ |
- (a)
Describe Describe how the student should use the measuring cylinder and thread to obtain the readings V₁ and V₂ accurately.
3 marks - (b)
Calculate Calculate the density of the stone. Give your answer to an appropriate number of significant figures.
3 marks - (c)
Suggest The stone is porous and slowly absorbs water. Suggest how this affects the value obtained for the density, and suggest one improvement to the method.
3 marks
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(a)
Describe Describe how the student should use the measuring cylinder and thread to obtain the readings V₁ and V₂ accurately.
Turn the task into a measurable method: name the independent, dependent and controlled quantities; describe apparatus and repeats; then explain how the evidence will be processed and how uncertainty or safety will be managed.
- 1
part-fill the cylinder with water and record the level V₁, reading the bottom of the meniscus with the eye level with the surface
- 2
lower the stone in gently on the thread so that no water splashes out and the stone is fully submerged
- 3
record the new level V₂ once the water is still
(b)
Calculate Calculate the density of the stone. Give your answer to an appropriate number of significant figures.
Turn the task into a measurable method: name the independent, dependent and controlled quantities; describe apparatus and repeats; then explain how the evidence will be processed and how uncertainty or safety will be managed.
- 1
V = V₂ − V₁ = 68.0 − 50.0 = 18.0 cm³
- 2
ρ = m / V = 47.6 / 18.0
- 3
ρ = 2.64 g/cm³ (2.6 g/cm³ also accepted; unit required)
(c)
Suggest The stone is porous and slowly absorbs water. Suggest how this affects the value obtained for the density, and suggest one improvement to the method.
Turn the task into a measurable method: name the independent, dependent and controlled quantities; describe apparatus and repeats; then explain how the evidence will be processed and how uncertainty or safety will be managed.
- 1
water enters the stone, so the rise in level V₂ − V₁ is smaller than the true volume of the stone
- 2
the calculated density is therefore too high
- 3
improvement: read V₂ immediately on submerging, or seal the stone first, or use a displacement can
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