Forces | OCR GCSE Combined Science Physics, Higher tier (J250)

Forces

320 questions
19 subtopics
Paper 11 (Physics)
Paper 11 (Physics)

Forces is examined in Paper 11 (Physics).

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, resolving forces, and free body diagrams, resultant forces, and balanced forces, newton's second law, and inertia, momentum and its conservation, work done, and stored energy, power, and Newton's third law, circular motion and changing velocity, 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 and calculations with weight and gravitational field strength.

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.
Resultant forces, and balanced forces

What does a resultant force do to an object that starts at rest?

Show the answer
It makes the object begin to accelerate in the direction of the resultant.
Momentum and its conservation

Is momentum a vector or a scalar quantity?

Show the answer
A vector, because it acts in the direction of the object's velocity.
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.
Stretching, bending and compressing; elastic and plastic

Describe the pair of forces that compress a pillar holding up a roof.

Show the answer
The weight of the roof pushes down on the top of the pillar while the ground pushes up on its base.

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, sloping and curved lines mean on a distance-time graph, what the gradient and area of a velocity-time graph give, and calculations of acceleration and distance from them.	16
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
Resolving forces, and free body diagrams	Resolving a force into two components at right angles, scale drawings and finding the size and direction of a resultant, forces in equilibrium, terminal velocity for a skydiver before and after the parachute opens, and why a car has a top speed that streamlining raises.	16
Resultant forces, and balanced forces	Finding the resultant of forces along one line, worked examples for rockets, trolleys, swimmers and lifts, what balanced forces mean, and why a zero resultant does not always mean rest.	16
Newton's second law, and inertia	The relationship between resultant force, mass and acceleration, what one newton means, calculations of force, mass and acceleration, and how inertial mass explains why loaded objects are harder to move.	16
Momentum and its conservation	How momentum is calculated from mass and velocity, its unit and why it is a vector, the law of conservation of momentum, and using it for trolleys that join after a collision, a snooker ball struck by another and two skaters pushing apart.	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
Circular motion and changing velocity	Why an object moving in a circle at steady speed has a changing velocity and is accelerating, the direction of the resultant force, and what supplies it for cars, strings and satellites.	10
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

Forces is 320 of the 1,222 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.