Models and rules: creating models and out into space
From Paper 1: Fundamentals of physics
211 mark
In a model ΔN = −λNΔt with N = 1000, λ = 0.10 s⁻¹ and Δt = 1.0 s, N after one step is:
From Paper 1: Fundamentals of physics
221 mark
A capacitor discharges with time constant 2.0 s. After 4.0 s the fraction of charge left is:
From Paper 1: Fundamentals of physics
231 mark
A 0.50 kg mass on a spring of stiffness 20 N m⁻¹ oscillates. The period is about:
From Paper 1: Fundamentals of physics
241 mark
A force of 4.0 N acts for 0.50 s. The change in momentum is:
From Paper 1: Fundamentals of physics
251 mark
At a distance 2R from the centre of a planet of radius R, g is:
From Paper 1: Fundamentals of physics
36(a)4 marks
A 1000 μF capacitor charged to 6.0 V discharges through 4.7 kΩ. Use one step of ΔQ = −(Q/RC)Δt with Δt = 1.0 s to estimate V after 1.0 s, compare with the exact value, and explain the difference.
From Paper 1: Fundamentals of physics
36(b)4 marks
Carbon-14 has a half-life of 5730 years. Living material has an activity of 0.25 Bq per gram of carbon. Calculate the age of a sample with activity 0.0625 Bq g⁻¹, and the activity of a sample 8000 years old.
From Paper 1: Fundamentals of physics
36(c)3 marks
Explain why capacitor discharge and radioactive decay are described by the same type of equation.
From Paper 1: Fundamentals of physics
37(a)4 marks
The Moon orbits at 3.84 × 10⁸ m from the Earth's centre with period 27.3 days. Calculate its centripetal acceleration and show it agrees with g/60² (the Moon is about 60 Earth radii away).
From Paper 1: Fundamentals of physics
37(b)4 marks
A rocket ejects 50 kg of exhaust gas per second at 2500 m s⁻¹. Calculate the thrust and explain it using conservation of momentum.
From Paper 2: Scientific literacy in physics
2(c)3 marks
Compare the electric field around a point charge with the gravitational field around a point mass.
From Paper 2: Scientific literacy in physics
6(a)4 marks
The top of a tall building sways with SHM of frequency 0.20 Hz and amplitude 0.30 m. Calculate the maximum speed and maximum acceleration.
From Paper 2: Scientific literacy in physics
6(b)4 marks
Explain why wind gusts can make the building resonate, and how a tuned mass damper reduces the motion.
Advance Notice article (written for this paper): Seeing inside the body with antimatter
(1) Positron emission tomography (PET) builds a three-dimensional map of where a radioactive tracer collects in the body. The most common tracer is a sugar labelled with fluorine-18, which decays by β⁺ emission with a half-life of 110 minutes.
(2) Because fluorine-18 decays so quickly, it is made in a cyclotron close to the hospital. A typical dose leaves the cyclotron at 08:00 with an activity of 2.0 GBq and is injected about two hours later.
(3) Each positron travels about a millimetre through tissue before it meets an electron. The pair annihilates, producing two gamma photons, each of energy 511 keV, which travel in almost exactly opposite directions.
(4) A ring of detectors surrounds the patient. When two detectors on opposite sides register photons within a few nanoseconds of each other, the annihilation must have happened somewhere on the line joining them. Modern scanners also measure the tiny difference in arrival times to locate the event along that line.
(5) A scan typically collects about 4 × 10⁸ such coincidences in 20 minutes. Like all counting experiments, the image is noisy: the uncertainty in N counts is about √N.
(6) A PET scan gives the patient an effective dose of about 7 mSv, compared with an average background dose in the UK of 2.7 mSv per year. The commonly used risk estimate is a 5% chance of a fatal cancer per sievert.
(7) PET shows what tissues are doing (for example, fast-growing tumours take up more sugar), while X-ray CT shows their structure. Many scanners combine the two.
From Paper 2: Scientific literacy in physics
8(c)4 marks
Calculate the activity of the dose in paragraph 2 when it is injected at 10:00.
From Paper 3: Practical skills in physics
3(a)3 marks
Describe how to use a datalogger to record the discharge of a capacitor through a resistor.
From Paper 3: Practical skills in physics
3(b)5 marks
The time for the pd to halve was 3.3 s with R = 10 kΩ. Calculate C and decide whether it matches the 470 μF ± 10% rating.
From Paper 3: Practical skills in physics
3(c)4 marks
Repeated halving times were 3.2, 3.3, 3.4 and 3.3 s. Estimate the uncertainty in C.
From Paper 3: Practical skills in physics
5(a)*6 marks
Plan an experiment to investigate how the damping of a pendulum depends on the area of a card attached to the bob.
From Paper 3: Practical skills in physics
5(b)6 marks
For one card, the amplitude fell from 100 mm to 50 mm in 5 oscillations, and to 25 mm after 10 oscillations.
(i) Show that the damping is exponential and calculate the ratio of successive amplitudes.
(ii) Predict the amplitude after 20 oscillations.
Score 0 / 63 · 0 of 19 marked
This paper is written by Plasmo in the style of the OCR A-Level Physics exam. It is not a past paper and is not produced or endorsed by the exam board.
creating models and out into space Exam Questions: OCR A-Level Physics | Plasmo