Physics on the move — OCR GCSE Physics
Test yourself on Physics on the move with OCR GCSE practice questions.
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Physics on the move explained
This recall target asks you to attach an order-of-magnitude speed to familiar moving things.
Read the full explanation
Learn benchmark values in metres per second and be ready to convert to km/h by multiplying by 3.6. Typical figures: walking about 1.5 m/s (roughly 5 km/h); running about 3–6 m/s; cycling about 5–10 m/s; a car on a motorway about 30 m/s (about 110 km/h); a train about 50–60 m/s; sound in air about 340 m/s; wind typically a few m/s up to about 20–30 m/s in a gale. Use these as anchors: a value wildly outside the band signals a wrong choice. Remember sound is far faster than any everyday road vehicle, and wind is usually slower than a cyclist.
estimate the magnitudes of everyday accelerations
Here you judge how quickly velocity changes in familiar situations, using acceleration = change in velocity ÷ time. A car going from rest to about 30 m/s in 10 s has an acceleration near 3 m/s². A bus pulling away gently is around 1 m/s²; hard braking can reach about 8–10 m/s². A dropped object accelerates at about 10 m/s² due to gravity. A train easing out of a station is small, perhaps 0.5 m/s². Use the formula to check an option: divide the velocity change by the time taken. Values far above 10 m/s² for ordinary road travel are unrealistic, and a negative value simply means slowing down.
make calculations using ratios and proportional reasoning to convert units and to compute rates (to include: conversion from non-SI to SI units)
Proportional reasoning means identifying which quantity is directly proportional to which and which is inversely proportional. For a rate such as speed = distance ÷ time, doubling distance at fixed time doubles the speed, but doubling time at fixed distance halves it, because time sits in the denominator. Convert non-SI units to SI before substituting: 1 km = 1000 m, 1 minute = 60 s, 1 hour = 3600 s, 1 g = 1 × 10⁻³ kg and 1 cm³ = 1 × 10⁻⁶ m³. For example, 72 km/h becomes 72 × 1000 ÷ 3600 = 20 m/s. Use ratio methods to scale consistently, keep track of which variable changes and which is held constant, and check that the computed rate has sensible SI units such as m/s or kg/m³.
explain methods of measuring human reaction times and recall typical results
Human reaction time is the delay between a stimulus and a response. A common method uses a ruler drop: one person holds a ruler vertically while a second person places a thumb and finger either side of the lower end without touching it; the holder releases the ruler without warning and the catcher closes the fingers to trap it. The distance the ruler falls is read from the scale, and a conversion table or the equation for free fall links drop distance to reaction time. Repeating the test and averaging reduces random error. Typical human reaction times are around 0.2 s to 0.3 s, with the ruler dropping roughly 20 cm to 45 cm. A second method uses a computer or stopwatch to time a response to a visual or sound signal, though a stopwatch adds the timer's own reaction delay.
explain the factors which affect the distance required for road transport vehicles to come to rest in emergencies and the implications for safety (to include: factors that affect thinking and braking distance and overall stopping distance)
Stopping distance is the total distance a vehicle travels from the moment a hazard is seen until it stops, and it is the sum of thinking distance and braking distance. Thinking distance depends on the driver's reaction time and the vehicle's speed: a tired, distracted or impaired driver reacts more slowly, and a faster vehicle covers more ground before the brakes are even applied. Braking distance depends on the speed of the vehicle, the mass of the vehicle and its load, the condition of the brakes and tyres, and the grip between the tyres and the road. Wet, icy or loose surfaces reduce grip and lengthen braking distance, while a heavier vehicle needs more force to decelerate. Because kinetic energy rises with the square of speed, doubling speed greatly increases braking distance.
estimate how the distances required for road vehicles to stop in an emergency, varies over a range of typical speeds (content found only in the physics separate science qualification)
Stopping distance is the total distance a vehicle travels from the moment the driver decides to brake until the vehicle stops. It has two parts: thinking distance, travelled at constant speed during the driver's reaction time, and braking distance, covered while the brakes decelerate the vehicle. Thinking distance grows in direct proportion to speed, because distance = speed × reaction time. Braking distance grows much faster, roughly with the square of the speed, because the kinetic energy that must be removed depends on speed squared. So doubling the speed roughly doubles thinking distance but roughly quadruples braking distance, and the total rises steeply. A typical reaction time of about 0.7 s gives a thinking distance of roughly 21 m at 30 m/s. Estimating means using sensible values and rounding, not quoting exact figures.
explain the dangers caused by large decelerations
A large deceleration means velocity changes quickly, so the rate of change of velocity is high. Since force equals mass times acceleration (F = m × a), a large deceleration requires a large resultant force on whatever is being slowed. In a vehicle, that force acts through the seat belt, airbag or crumple zone on the occupants. A large deceleration over a short time gives a large force, which can cause injury such as whiplash, internal damage or fractures, and can throw loose objects forward. Spreading the same change in velocity over a longer time reduces the deceleration and therefore the force, which is why crumple zones, seat belts and airbags are designed to extend the stopping time. Learners should link the size of the deceleration to the size of the force and then to the risk of harm.
estimate the forces involved in typical situations on a public road (content found only in the physics separate science qualification) (Higher tier only)
This statement applies only to the separate physics qualification and only at Higher tier. Learners estimate the forces in everyday road situations by using F = m × a, choosing sensible values for mass and acceleration or deceleration. For a car of about 1000 kg braking from 20 m/s to rest in 4 s, the deceleration is 20 ÷ 4 = 5 m/s², so the force is about 1000 × 5 = 5000 N. Estimates should be rounded to one or two significant figures and stated with units. Learners should recognise that a heavier vehicle or a shorter stopping time gives a larger force, and should judge whether an answer is of a reasonable order of magnitude for a public road.
estimate, for everyday road transport, the speed, accelerations and forces involved in large accelerations (content found only in the physics separate science qualification)
This separate-science criterion asks you to make order-of-magnitude estimates for everyday road transport, covering three linked quantities: speed, acceleration and the force needed for a large acceleration. Start from familiar speeds: a car on a motorway travels at roughly 30 m/s (about 70 mph), and a town speed of 30 mph is about 13 m/s. For a large acceleration, take a car reaching 27 m/s from rest in about 9 s, giving a ≈ 3 m/s². Then use F = ma with a mass near 1200 kg to get F ≈ 3600 N, roughly 4 kN. Check units: m/s for speed, m/s² for acceleration, N for force. Round to one significant figure and state your assumptions, because an estimate is judged on sensible values and clear reasoning, not on a single exact answer.
Your focus
- State typical speeds for wind, sound, walking, running and cycling.
- Compare everyday speeds by order of magnitude.
- Convert a speed between m/s and km/h accurately.
Show all 27 objectives
- Estimate everyday accelerations using change in velocity over time.
- Compare road, rail and free-fall accelerations by magnitude.
- Interpret the sign of an acceleration as speeding up or slowing down.
- Convert non-SI quantities such as km/h and g to SI units
- Predict the effect on a rate of changing a numerator or denominator variable
- Compute rates accurately and state the correct SI unit
- Explain how a ruler-drop test measures human reaction time.
- Describe how drop distance is converted into a reaction time.
- Recall a typical value for human reaction time with its unit.
- Explain how driver reaction time and speed affect thinking distance
- Explain how speed, mass, brake and tyre condition and road grip affect braking distance
- Explain how overall stopping distance relates to safety in emergency situations
- Identify the two components of stopping distance and state how they combine.
- Describe how thinking distance and braking distance each change as speed increases.
- Estimate a stopping distance for a typical speed using a sensible reaction time.
- Explain why a large deceleration produces a large force on a passenger
- Describe how a large force can cause injury in a collision
- Explain how increasing the stopping time reduces the danger
- Estimate the force on a vehicle in a typical road situation using F = m × a
- Choose realistic values for mass and acceleration or deceleration
- Judge whether an estimated force is reasonable for a public road
- Estimate a typical speed for everyday road transport in m/s.
- Calculate an acceleration from a chosen speed change and time.
- Estimate the force involved in a large acceleration using F = ma.
Physics on the move exam tips
Marking Points
- Selects a value of about 340 m/s for the speed of sound in air.
- Chooses a walking speed of roughly 1.5 m/s rather than a vehicle speed.
- Matches a cyclist to a value of roughly 5–10 m/s.
- Assigns a motorway car speed of about 30 m/s.
- Converts between m/s and km/h correctly using a factor of 3.6.
- Rejects an option that gives wind a speed greater than sound.
- Applies acceleration = change in velocity ÷ time to test a proposed value.
- Estimates a car accelerating from rest to about 30 m/s in 10 s as roughly 3 m/s².
- Recognises free fall near the Earth's surface as about 10 m/s².
- Assigns gentle public-transport acceleration a value near or below 1 m/s².
- Interprets a negative acceleration as deceleration during braking.
- Rejects an everyday road acceleration far greater than 10 m/s².
- Identifies whether a named quantity is directly or inversely proportional to the variable being changed before predicting the effect on the rate
- Converts non-SI units to SI using the correct factor, for example 72 km/h to 20 m/s or 250 g to 0.25 kg
- Computes a rate by dividing the correct numerator by the correct denominator and attaches the correct SI unit
- Explains that doubling a denominator variable at fixed numerator halves the rate, whereas doubling a numerator variable doubles it
- Describes the ruler-drop method with one person holding and releasing the ruler and another catching it between thumb and finger.
- Explains how the drop distance is converted to a reaction time using a table or the free-fall relationship.
- States that repeating the measurement and averaging improves reliability by reducing random error.
- Recalls that typical human reaction times are of the order of 0.2 s to 0.3 s.
- States that stopping distance equals thinking distance plus braking distance
- Explains that thinking distance increases with speed and with a longer driver reaction time
- Identifies driver factors such as tiredness, distraction, alcohol or drugs that increase reaction time
- Explains that braking distance increases with the mass or load of the vehicle
- Explains that poor road grip from wet, icy or loose surfaces increases braking distance
- Relates a longer overall stopping distance to a higher risk of collision and links this to a safety measure
- States that stopping distance equals thinking distance plus braking distance.
- Explains that thinking distance increases in proportion to speed because it equals speed multiplied by reaction time.
- Explains that braking distance increases roughly with the square of speed because kinetic energy depends on speed squared.
- Estimates that doubling speed roughly doubles thinking distance but roughly quadruples braking distance.
- Uses a typical reaction time and a chosen speed to estimate a thinking distance numerically.
- States that a large deceleration means a large rate of change of velocity
- Links a large deceleration to a large resultant force using F = m × a
- Explains that a large force acting on a passenger can cause injury
- Identifies that extending the time of deceleration reduces the force and the danger
- Selects realistic values for mass and for acceleration or deceleration in a road situation
- Applies F = m × a correctly to the chosen values
- Rounds the estimated force to a sensible number of significant figures and gives the unit in newtons
- Compares estimates and explains why a heavier vehicle or shorter stopping time gives a larger force
- Selects a realistic everyday road speed such as about 13 m/s in town or about 30 m/s on a motorway.
- Calculates acceleration from a chosen change in speed and time using a = Δv ÷ t with consistent units.
- Applies F = ma with a sensible vehicle mass to estimate the force for a large acceleration.
- Rounds estimates to one or two significant figures and states the assumptions behind them.
- Keeps units consistent, quoting speed in m/s, acceleration in m/s² and force in N or kN.
Examiner Tips
- 💡Memorise a small set of anchor values and compare each option against them.
- 💡Check units before choosing: an answer in km/h needs converting to compare with m/s figures.
- 💡Eliminate options that are orders of magnitude out before deciding between close ones.
- 💡Substitute the velocity change and time into the formula before choosing an option.
- 💡Sanity-check the answer against the 10 m/s² free-fall benchmark.
- 💡Watch the sign: deceleration is a negative acceleration.
- 💡Write the rate equation first, then mark which symbol is on top and which is underneath before reasoning about proportional change
- 💡Convert all non-SI values to SI in a separate line so a unit slip is easy to spot
- 💡Check the final unit against the quantity, for example m/s for speed and kg/m³ for density
- 💡Name both roles in the ruler-drop test and say the ruler is released without warning.
- 💡Explain that the distance fallen, not the time, is what is read from the scale.
- 💡Quote a typical value with its unit, such as about 0.25 s, to show recall.
- 💡Structure the answer around thinking distance, braking distance and then overall stopping distance so every clause of the question is covered
- 💡Use a concrete example such as a wet road or a tired driver to show how a factor changes the distance
- 💡Finish by linking the longer distance to a safety implication, such as a higher chance of a collision or the value of speed limits
- 💡Write the relationship stopping distance = thinking distance + braking distance before substituting any numbers.
- 💡Show the estimate step by step: pick a reaction time, calculate speed × time, then state how braking distance scales with speed squared.
- 💡Round sensibly and state that the answer is an estimate, since reaction time and braking vary between drivers and vehicles.
- 💡Check the trend: at higher speed the total stopping distance should rise faster than the speed itself.
- 💡Name the equation F = m × a and say what each symbol means before applying it
- 💡Use a road example such as a car braking hard or hitting a barrier to make the link between deceleration and force concrete
- 💡When asked about safety features, explain how each one increases the time taken to stop
- 💡Write down the values you choose for mass and acceleration before substituting them into F = m × a
- 💡Show the substitution and the arithmetic so the estimate can be followed
- 💡Check the order of magnitude of your answer against everyday experience of road vehicles
- 💡Write down your assumed values before calculating so the examiner can follow your reasoning.
- 💡Round to one significant figure for an estimate and say 'approximately' with the unit.
- 💡Sanity-check the answer: a few kN is a reasonable force for a family car accelerating hard.
Common Mistakes
- Confuses the speed of sound with the speed of light; keep sound at about 340 m/s in air.
- Gives walking a speed of tens of metres per second; keep it near 1.5 m/s.
- Forgets to multiply by 3.6 when converting m/s to km/h; apply the factor to every conversion.
- Treats wind as faster than a car on a motorway; keep typical wind well below 30 m/s.
- Divides time by velocity change; divide the velocity change by the time instead.
- Gives a braking car a positive acceleration while calling it slowing; treat slowing as negative acceleration.
- Estimates free fall as far from 10 m/s²; keep it near 10 m/s².
- Assigns a bus the same acceleration as a hard-braking car; keep gentle starts near 1 m/s².
- States that doubling any variable doubles the rate; check whether the variable is in the numerator or the denominator before predicting the change
- Converts kilometres to metres but leaves time in minutes; convert every quantity to SI before dividing
- Multiplies by a conversion factor in the wrong direction, for example dividing by 1000 when changing km to m; write the factor as a fraction so the unwanted unit cancels
- Claims the ruler measures time directly; read the drop distance and convert it to a reaction time.
- Omits the need for the catcher to be unprepared; a warned catcher gives an unrealistically short time.
- Gives a typical reaction time of several seconds; human reaction times are around 0.2 s to 0.3 s.
- Adds thinking distance and braking distance incorrectly; state clearly that stopping distance is their sum
- Treats reaction time as a property of the brakes; keep reaction time as a driver factor affecting thinking distance
- Assumes braking distance is proportional to speed; explain that it rises much faster than speed because kinetic energy depends on speed squared
- Ignores road surface when discussing braking; include grip between tyres and road as a key factor
- Treats stopping distance as only the braking distance; add the thinking distance travelled during the reaction time.
- Assumes braking distance doubles when speed doubles; recognise that it rises roughly with the square of speed.
- Uses a reaction time of zero; choose a realistic value such as about 0.7 s.
- Adds speeds rather than distances when combining the two parts; add the two distances.
- Confuses deceleration with speed; keep the distinction between speed, velocity and rate of change of velocity
- Assumes a large deceleration produces a small force; apply F = m × a so a larger deceleration gives a larger force
- Ignores the role of time; explain that spreading the change over a longer time lowers the deceleration and the force
- Uses an unrealistic mass such as 10 kg for a car; choose a value of the order of 1000 kg
- Forgets to convert a stopping time or speed into consistent units; keep seconds and metres per second throughout
- Gives an answer without a unit; state the force in newtons and round to a sensible number of significant figures
- Uses a speed in mph directly in a calculation; convert to m/s first, for example 30 mph ≈ 13 m/s.
- Forgets to square or misapplies units for acceleration; acceleration is measured in m/s², not m/s.
- Omits the vehicle mass when estimating force; state a mass such as 1200 kg before applying F = ma.