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CIE iGCSE Co-Ordinated Science P1.5.3 Centre of gravity Exam Style Questions Paper 3

CIE iGCSE Co-Ordinated Science Paper 3 - All Chapters

Question

(a) A student walks to school.
Fig. 9.1 shows a speed–time graph for part of the journey.
(i) Write the letter C on a part of the graph where the student is walking at constant speed.
(ii) State a time when the student accelerates.
(iii) State the maximum speed of the student.
(b) In the classroom, the student uses a laptop computer.
Fig. 9.2 shows the power cable from the mains supply to the laptop.
The power cable insulation is damaged.
State one danger of using this laptop with damaged insulation.
(c) Fig. 9.3 shows a ray of light reflecting off the laptop screen.
(i) On Fig. 9.3, label the angle of incidence with the letter \(i\) and the angle of reflection with the letter \(r\).
(ii) State the relationship between the angle of incidence and the angle of reflection.
(d) The student watches the teacher demonstrate an experiment using the isotope strontium-90. Strontium-90 is radioactive and emits \(\beta\)-particles.
(i) State the charge on a \(\beta\)-particle.
(ii) State one method of storing safely a small quantity of strontium-90 in a school.
(e) Fig. 9.4 shows the student sitting on a chair.
Fig. 9.5 shows the student balancing on the chair which is tilted backwards.
Explain why the student and chair fall over when the chair is tilted further backwards. Use ideas about centre of gravity and moments in your answer.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P1.2 — Motion (Part (a))
• Topic P4.4 — Electrical safety (Part (b))
• Topic P3.2.1 — Reflection of light (Part (c))
• Topic P5.2.2 — The three types of nuclear emission (Part (d)(i))
• Topic P5.2.5 — Applications and safety precautions (Part (d)(ii))
• Topic P1.5.2 & P1.5.3 — Turning effect of forces & Centre of gravity (Part (e))

▶️ Answer/Explanation

(a)(i) C anywhere between t = 0 and t = 400 or between t = 440 and t = 800

Constant speed is shown by a horizontal line on a speed-time graph. The graph has two horizontal sections: from 0 to 400 seconds and from 440 to 800 seconds.

(a)(ii) anywhere from t = 400 s to t = 440 s

Acceleration is shown by a line with a positive gradient (sloping upwards). The graph shows this between 400 and 440 seconds, where the speed increases from 0.2 m/s to 0.4 m/s.

(a)(iii) 0.4 m/s

The maximum speed is the highest point on the graph, which is 0.4 m/s.

(b) electrocution/electric shock

Damaged insulation exposes the live wire inside the cable. If a person touches the exposed wire, they could receive an electric shock or be electrocuted, which can be fatal.

(c)(i) i and r labelled correctly on the figure

The angle of incidence (\(i\)) is the angle between the incident ray and the normal (a line perpendicular to the surface at the point of reflection). The angle of reflection (\(r\)) is the angle between the reflected ray and the normal.

(c)(ii) angle of incidence = angle of reflection

This is the law of reflection: the angle of incidence is always equal to the angle of reflection.

(d)(i) negative/minus 1 / –

Beta particles (\(\beta^-\)) are high-speed electrons emitted from the nucleus. They have a relative charge of -1.

(d)(ii) in a lead container

Radioactive sources should be stored in lead containers. Lead is dense and absorbs the radiation, shielding people from exposure. The container should also be labelled with a radiation warning symbol.

(e) The centre of gravity is not over the base; a moment is produced by the weight.

For an object to be stable, its centre of gravity must be above the area of its base. When the chair is tilted backwards, the centre of gravity moves outside the base. The weight of the student and chair then acts at a distance from the pivot (the edge of the base), creating a turning effect (moment). This moment causes the student and chair to fall over.

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