Sara Bentley
Cambridge IGCSE™ PHYSICS 0625/42
Question 1
(a) Speed–Time Graph Analysis [cite: 2]
(i) Motion descriptions:
- A and B: Constant acceleration [cite: 1]
- C and D: Constant speed / velocity [cite: 1]
- D and E: Increasing deceleration [cite: 1]
(ii) Calculate the distance travelled between time t = 0 and time t = 18 s:
distance = 130 m [cite: 1]
(b) Vectors & Scalars [cite: 2]
(i) Definition complete sentence: A vector quantity has magnitude (size) and direction [cite: 1].
(ii) Vector quantities from list [cite: 2]:
- acceleration [cite: 1]
- mass
- electric field strength [cite: 1]
- time
- weight [cite: 1]
- energy
Question 2
(a) Satellite Orbit & Rocket Acceleration [cite: 2]
(i) Direction of force on satellite: Perpendicular to motion / towards the centre of the orbit [cite: 1].
(ii) Initial acceleration calculation:
F = (1.9 × 10⁵ N) – (1.5 × 10⁴ kg × 9.8 N/kg) = 43 000 N [cite: 1]
Acceleration a = F / m = 43 000 N / (1.5 × 10⁴ kg) = 2.867 m/s² ≈ 2.9 m/s² [cite: 1]
acceleration = 2.9 m/s² [cite: 1]
(b) Pressure & Temperature Conversion [cite: 2]
(i) Pressure in terms of particles [cite: 2]: Helium gas particles move rapidly and collide with the inside walls of the balloon [cite: 1]. These collisions exert a force per unit area, which generates pressure [cite: 1].
(ii) Temperature conversion (228 K to °C) [cite: 2]:
temperature = -45 °C [cite: 1]
Question 3
(a) Electric Shower Thermal Energy [cite: 2]
(i) Mass of water proof [cite: 2]:
(ii) Required energy calculation [cite: 2]:
E = m × c × ΔT = 18 kg × 4200 J/(kg °C) × 23 °C = 1.7388 × 10⁶ J ≈ 1.7 × 10⁶ J [cite: 1]
energy = 1.7 × 10⁶ J [cite: 1]
(iii) Power transferred calculation [cite: 2]:
Power P = E / t = 1.7 × 10⁶ J / 240 s = 7083 W ≈ 7100 W [cite: 1]
power = 7100 W [cite: 1]
(b) Shower Temperature Variance [cite: 2]
Reason for higher water temperature: Initial inlet temperature of the water increased OR water flow rate decreased [cite: 1].
Question 4
(a) Impulse Definition [cite: 2]
Impulse is defined as force × time (or change in momentum) [cite: 1].
(b) Landing Mechanics & Pressure [cite: 2]
(i) Resultant force calculation [cite: 2]:
resultant force = 270 N [cite: 1]
(ii) Function of bending knees [cite: 2]: Bending knees increases the time taken to stop moving [cite: 1]. For the same change in momentum (impulse) [cite: 1], an increased stopping time reduces the resultant force on the student [cite: 1].
(iii) Pressure calculation [cite: 2]:
pressure = 1.4 | unit = N/cm² [cite: 1]
Question 5
(a) Evaporative Cooling Mechanism [cite: 2]
Thermal energy transfers from skin to water [cite: 1]. The most energetic (fastest) water molecules evaporate from the liquid surface [cite: 1]. The remaining water molecules have a lower average kinetic energy, lowering the temperature of the remaining water and cooling the skin [cite: 1].
(b) Evaporation Factors [cite: 2]
- Air temperature [cite: 1]
- Wind speed / air movement (or surface area / humidity) [cite: 1]
Question 6
(a) Principal Focus Definition [cite: 2]
The principal focus of a lens is a point on the principal axis where rays parallel to the principal axis converge after passing through the lens [cite: 1].
(b) Ray Diagram Construction [cite: 2]
- Ray 1: Parallel to principal axis from top of object O to lens center, refracting through principal focus F on the right [cite: 1].
- Ray 2: Straight line from top of object O through optical center of lens without bending [cite: 1].
- Image: Inverted arrow drawn from principal axis to the intersection point, labeled I [cite: 1].
(c) Electromagnetic Spectrum [cite: 2]
Region with lowest frequency: Radio waves [cite: 1]
Question 7
(a) Loudspeaker & Sound Wavelength [cite: 2]
(i) Complete sentences [cite: 2]:
A changing magnetic field is produced by the alternating current (a.c.) in the coil [cite: 1]. This magnetic field interacts with the magnetic field due to the (permanent) magnet [cite: 1]. This causes the cone to vibrate. The vibration of the cone / air particles transfers energy to a student as sound [cite: 1].
(ii) Wavelength calculation [cite: 2]:
wavelength = 0.77 | unit = m [cite: 1]
(b) Ultrasound Definition [cite: 2]
Sound waves with a frequency higher than 20 000 Hz (20 kHz), above the upper limit of human hearing [cite: 1].
Question 8
(a) Electric Fields [cite: 2]
(i) Definition [cite: 2]: An electric field is a region where an electric charge / charged particle experiences an electrostatic force [cite: 1].
(ii) Field lines between parallel plates [cite: 2]: 4 straight, parallel, evenly spaced lines perpendicular to the plates, with arrows pointing upwards (from positive to negative plate) [cite: 1].
(b) Relay Circuit & Charge [cite: 2]
(i) Component X [cite: 2]: Fuse [cite: 1]
(ii) Explanation sentences [cite: 2]: When the temperature of the thermistor increases, the resistance of the thermistor decreases [cite: 1]. This causes the p.d. across the relay coil to increase [cite: 1]. The magnetic field produced by the relay coil gets stronger [cite: 1]. The relay coil attracts the switch / iron armature, which causes the lamp to light [cite: 1].
(iii) Charge calculation [cite: 2]:
charge = 380 C [cite: 1]
Question 9
(a) Isotopes & Radioactive Decay [cite: 2]
(i) Nuclear composition [cite: 2]:
- Similarity: Same number of protons [cite: 1]
- Difference: Different number of neutrons [cite: 1]
(ii) Sketch graph [cite: 2]: Smooth curve starting at (0 yr, 16 µg), passing through (5700 yr, 8 µg) and (11400 yr, 4 µg) [cite: 1].
(b) Environmental Radiation [cite: 2]
Ionising nuclear radiation that is always present in the environment is known as background radiation [cite: 1].
(c) Background Source [cite: 2]
Radon gas (or rocks / building materials / cosmic rays) [cite: 1].
Question 10
(a) Nuclear Fission & Power Generation [cite: 2]
(i) Fission process [cite: 2]: A slow-moving neutron collides with and is absorbed by a heavy nucleus [cite: 1]. The nucleus splits into two smaller daughter nuclei, releasing neutrons and large amounts of kinetic and thermal energy [cite: 1].
(ii) Complete sentences [cite: 2]: Thermal energy is used to heat water to produce steam at high pressure [cite: 1]. This drives a turbine connected to a generator [cite: 1].
(iii) Solar vs Nuclear comparison [cite: 2]:
- Advantage: Reliable, continuous power supply unaffected by weather / day-night cycles [cite: 1].
- Disadvantage: Produces radioactive waste requiring safe, long-term disposal [cite: 1].
(b) Non-Solar Energy Source [cite: 2]
Tidal energy or Geothermal energy [cite: 1].
Question 11
(a) Astronomical Timescales Matching [cite: 2]
- Earth orbits the Sun once ➔ 365 days [cite: 1]
- Earth rotates once on its axis ➔ 24 hours [cite: 1]
- Light travels from Sun to Earth ➔ 8.3 minutes [cite: 1]
- Moon orbits the Earth once ➔ 1 month [cite: 1]
(b) Orbital Period of Jupiter Proof [cite: 2]
Time T in hours = d / v = 4.8883 × 10⁹ km / (4.70 × 10⁴ km/h) = 104 007 hours [cite: 1]
Time T in years = 104 007 / (24 × 365) = 11.87 years ≈ 11.9 years [cite: 1]
(c) Light-Year & Galactic Speed [cite: 2]
(i) Light-year definition [cite: 2]: The distance travelled by light in a vacuum in one year [cite: 1].
(ii) Galactic recession speed calculation [cite: 2]:
Distance d = 1.6 × 10⁸ × 9.46 × 10¹⁵ m = 1.5136 × 10²⁴ m [cite: 1]
Speed v = H₀ × d = (2.2 × 10⁻¹⁸ s⁻¹) × (1.5136 × 10²⁴ m) = 3.33 × 10⁶ m/s ≈ 3.3 × 10⁶ m/s [cite: 1]
speed = 3.3 × 10⁶ m/s [cite: 1]
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