CIE iGCSE Co-Ordinated Science P1.5.2 Turning effect of forces Exam Style Questions Paper 3
Question
Topic codes:
• Topic P1.2 — Motion (Part (a)(i) & (a)(ii))
• Topic P2.1.2 — Particle model (Part (b))
• Topic P1.5.2 — Turning effect of forces (Part (c))
• Topic P4.2.1 — Electrical charge (Part (d)(i), (d)(ii) & (d)(iii))
▶️ Answer/Explanation
(a)(i) Any time between t = 0 to t = 40 s
The car is accelerating when the speed is increasing. From the graph, the speed increases from 0 to 8 m/s during the first 40 seconds (the line slopes upwards). Any time within this interval shows acceleration.
(a)(ii) 560 m
Total distance travelled = area under the speed-time graph.
The graph forms a trapezium split into three sections:
- Triangle 1 (0 to 40 s): \(\frac{1}{2} \times 40 \times 8 = 160\) m
- Rectangle (40 to 80 s): \(40 \times 8 = 320\) m
- Triangle 2 (80 to 100 s): \(\frac{1}{2} \times 20 \times 8 = 80\) m
Total distance = 160 + 320 + 80 = 560 m
(b) Particles move faster / have greater kinetic energy / \(E_k\)
As temperature increases, the air particles gain kinetic energy. They move more rapidly, colliding with each other and the tyre walls more frequently and with greater force. This increased motion causes the pressure in the tyre to rise.
(c) Moment = 720 Ncm
Moment = force × perpendicular distance from the pivot.
Moment = 40 N × 18 cm = 720 Ncm
(Note: The perpendicular distance is measured from the pivot to the line of action of the force. Here it is given as 18 cm.)
(d)(i) Friction
As the car moves, friction between the car and the air, and between the tyres and the road, causes the transfer of electrostatic charges. This is similar to charging by friction where electrons are transferred from one surface to another.
(d)(ii) Electrons
The charged particles that move during the transfer of electrostatic charge are electrons. They are negatively charged and are transferred from one material to another during friction.
(d)(iii) \(-1\)
Electrons have a relative charge of \(-1\). This means they have a negative charge equal in magnitude to the positive charge of a proton (\(+1\)).
Question
The energy is stored in a battery in the car.
The battery supplies a current of 96 A at 120 V to the motor that drives the car.
The tyre exerts a pressure of 20 N/cm² on the road.
Calculate the force exerted by the tyre on the road.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P6.1 — The Solar System (Part (a))
• Topic P4.2.5 — Electrical energy and electrical power (Part (b)(i))
• Topic P4.2.2 — Electric current (Part (b)(ii))
• Topic P1.5.2 — Turning effect of forces (Part (c)(i))
• Topic P1.7 — Pressure (Part (c)(ii))
▶️ Answer/Explanation
(a)(i) Gravitational attraction
The Sun’s gravitational field provides the centripetal force that keeps the Earth in its nearly circular orbit around the Sun.
(a)(ii) Milky Way
The Sun is one of approximately 100–400 billion stars in the Milky Way galaxy, which is a spiral galaxy about 100,000 light-years in diameter.
(b)(i) Energy = \(I \times V \times t = 96 \times 120 \times 900 = 10,368,000 \text{ J} \approx 10,000,000 \text{ J}\)
The electrical energy transferred is calculated using the formula \(E = IVt\), where current is in amperes, voltage in volts, and time in seconds. The unit of energy is the joule (J).
(b)(ii) Direct current (d.c.) flows in one direction only, whereas alternating current (a.c.) periodically changes direction.
In a direct current circuit, electrons flow continuously in the same direction. In an alternating current circuit, the direction of electron flow reverses periodically (e.g., 50 times per second in mains electricity).
(c)(i) moment = \(300 \times 0.40 = 120 \text{ N m}\)
The moment of a force is calculated using the equation \(\text{moment} = \text{force} \times \text{perpendicular distance from the pivot}\). The unit is newton-metre (N m).
(c)(ii) force = \(20 \times 180 = 3600 \text{ N}\)
Pressure is defined as force per unit area. The force can be calculated by multiplying pressure by area: \(\text{force} = \text{pressure} \times \text{area}\).