Forces | OCR GCSE Physics A, Foundation tier (J249)

Forces

309 questions
19 subtopics
Paper 1
Paper 1

Forces is examined in Physics A Paper 1.

It covers measuring distance and time, and calculating speed, converting units, and rates, vectors and scalars in motion, distance-time and velocity-time graphs, average speed, and the equations of uniform motion, how objects interact, and forces as vectors, newton's first law, newton's second law, force and the time taken to change velocity, work done, and stored energy, power, and Newton's third law, stretching, bending and compressing; elastic and plastic, force and extension, linear and non-linear, the spring constant, and work done in stretching, gravitational fields, weight and free fall, calculations with weight and gravitational field strength, turning forces and the moment of a force, levers and gears and pressure in fluids, and the force on a surface.

Sample questions from Forces

Answer each one closed book first, then open the answer.

Measuring distance and time, and calculating speed

A cyclist travels 450 m in 30 s. What is her average speed?

Show the answer
450 ÷ 30 = 15 m/s.
Vectors and scalars in motion

Which of speed and velocity is the vector, and what extra information does it carry?

Show the answer
Velocity is the vector, and it carries the direction of travel as well as the size of the speed.
Average speed, and the equations of uniform motion

A train covers 60 km at an average speed of 25 m/s. How long does the journey take?

Show the answer
60000 ÷ 25 = 2400 s, which is 40 minutes.
Newton's first law

What three changes to an object's motion can a resultant force produce?

Show the answer
It can make the object speed up, slow down, or change direction.
Force and the time taken to change velocity

Why does taking longer to bring a moving object to rest reduce the force acting on it?

Show the answer
The same change of velocity spread over a longer time gives a smaller acceleration, and force is mass × acceleration.
Power, and Newton's third law

A student does 1500 J of work running up a flight of stairs in 6 s. What is her useful power output?

Show the answer
1500 ÷ 6 = 250 W.
Force and extension, linear and non-linear

What does it mean if force and extension have a linear relationship?

Show the answer
Equal increases in force always produce equal increases in extension, so the graph of force against extension is a straight line through the origin.
Gravitational fields, weight and free fall

Define the weight of an object.

Show the answer
It is the force acting on the object because of the gravitational field it is in.

The 19 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Measuring distance and time, and calculating speed	Instruments for measuring length and time, why light gates beat a hand-held stopwatch, how reaction time is reduced, and finding speed from distance, time and the gradient of a distance-time graph.	28
Converting units, and rates	The standard units of distance and time, converting kilometres per hour to metres per second, minutes to seconds and centimetres to metres, and why units must match in an equation.	21
Vectors and scalars in motion	The difference between a scalar and a vector, why distance is a scalar and displacement a vector, how velocity differs from speed, and journeys where the two disagree.	10
Distance-time and velocity-time graphs	What horizontal, steeper and curving lines mean on a distance-time graph, what the gradient and horizontal or downward-sloping lines show on a velocity-time graph, calculating acceleration from the gradient, and describing a journey from its graph.	8
Average speed, and the equations of uniform motion	How average speed is found for a changing journey, distance, speed and time calculations, acceleration from a change in velocity, and the equation linking final velocity, starting velocity, acceleration and distance.	23
How objects interact, and forces as vectors	The four ways objects interact and which act at a distance, normal contact force and friction, the equal and opposite pair of forces produced by every interaction, free body force diagrams, and finding the resultant of forces acting along one line.	21
Newton's first law	What happens to an object with no resultant force on it, what a resultant force can change, and why spacecraft, books, cyclists and sliding loads behave as they do.	10
Newton's second law	The relationship between resultant force, mass and acceleration, what one newton means, calculations of force, mass and acceleration for trolleys, cars and balls, and why a loaded lorry accelerates more slowly than an empty one under the same driving force.	9
Force and the time taken to change velocity	Acceleration as change in velocity over time, the resultant force needed to change the velocity of a car or a ball in a given time, how fast a go-kart moves after a force has acted, and why crumple zones and padded landing mats lower the force by lengthening the time taken to stop.	8
Work done, and stored energy	How work done is calculated and its unit, why holding a bag still does no work, where energy goes when work is done against friction, and the energy in a moving object's kinetic store.	16
Power, and Newton's third law	The definition and unit of power with calculations for motors, lamps and stairs, the law describing interaction pairs, and why the two forces of a pair never cancel each other.	16
Stretching, bending and compressing; elastic and plastic	The three ways forces change shape and why at least two forces are needed, the forces that stretch a spring, bend a diving board and compress a pillar, elastic and plastic deformation and how to tell them apart, and why an overstretched spring stays longer.	16
Force and extension, linear and non-linear	Extension and how to calculate it, direct proportion up to the limit of proportionality, the elastic limit, linear and non-linear force-extension graphs, and the spring-stretching investigation with its variables, precautions, results table, hypothesis, length against force graph and conclusion.	29
The spring constant, and work done in stretching	What the spring constant measures and its unit, force = spring constant × extension with calculations and stiffness comparisons, work done in stretching as stored energy, work done = ½ × spring constant × extension², the area under a force-extension graph, and the effect of doubling the extension.	17
Gravitational fields, weight and free fall	Gravitational fields around every mass and why they only attract, field strength on the Earth and the Moon, weight as a force measured in newtons with a newtonmeter, how mass differs from weight, the centre of mass, and free fall at about 10 m/s² whatever the mass.	21
Calculations with weight and gravitational field strength	The relationship between weight, mass and gravitational field strength, its rearrangements, worked examples on the Earth and a moon, and how weight and mass behave when the field strength changes.	10
Turning forces and the moment of a force	What a pivot is and when a force makes an object turn, the direction of rotation, the moment of a force and its unit, calculations of moment, force and perpendicular distance, and the principle of moments applied to balanced see-saws.	17
Levers and gears	What a lever and a force multiplier are, how a lever, a long spanner and a crowbar multiply force, where the pivot, load and effort sit in a wheelbarrow, and what gears do.	11
Pressure in fluids, and the force on a surface	Why an inflated balloon holds a rounded shape, why wide snowshoes stop a walker sinking into deep snow and how a hydraulic system multiplies a force.	18

Forces is 309 of the 1,303 questions in the guide.Get the guide, £7

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.