Edexcel IGCSE Physics Forces, movement, shape and momentum questions

Forces, movement, shape and momentum syllabus

Questions on forces, movement, shape and momentum can test recall, calculations, explanations, diagrams, data handling and practical skills. You should be able to:

• 1.11 describe the effects of forces between bodies such as changes in speed, shape or direction
• 1.12 identify different types of force such as gravitational or electrostatic
• 1.13 understand how vector quantities differ from scalar quantities
• 1.14 understand that force is a vector quantity
• 1.15 calculate the resultant force of forces that act along a line
• 1.16 know that friction is a force that opposes motion
• 1.17 know and use the relationship between unbalanced force, mass and acceleration: force = mass × acceleration F = m × a
• 1.18 know and use the relationship between weight, mass and gravitational field strength: weight = mass × gravitational field strength W = m × g
• 1.19 know that the stopping distance of a vehicle is made up of the sum of the thinking distance and the braking distance
• 1.20 describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time
• 1.21 describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity)
• 1.22 practical: investigate how extension varies with applied force for helical springs, metal wires and rubber bands
• 1.23 know that the initial linear region of a force-extension graph is associated with Hooke’s law
• 1.24 describe elastic behaviour as the ability of a material to recover its original shape after the forces causing deformation have been removed
• 1.25P know and use the relationship between momentum, mass and velocity: momentum = mass × velocity p = m × v
• 1.26P use the idea of momentum to explain safety features
• 1.27P use the conservation of momentum to calculate the mass, velocity or momentum of objects
• 1.28P use the relationship between force, change in momentum and time taken: force = change in momentum / time taken F = (mv − mu) / t
• 1.29P demonstrate an understanding of Newton’s third law
• 1.30P know and use the relationship between the moment of a force and its perpendicular distance from the pivot: moment = force × perpendicular distance from the pivot
• 1.31P know that the weight of a body acts through its centre of gravity
• 1.32P use the principle of moments for a simple system of parallel forces acting in one plane
• 1.33P understand how the upward forces on a light beam, supported at its ends, vary with the position of a heavy object placed on the beam

How to answer forces, movement, shape and momentum questions

1. Read both axes and their scales before taking a gradient or area from a graph.
2. Choose a relationship that contains the quantity asked for and rearrange it before substituting.
3. For force questions, state the direction as well as the size of a resultant or acceleration.
4. Link each stage of an explanation: cause, physical change and observed outcome.

Forces, movement, shape and momentum example questions and worked answers

These examples show how information in a diagram, graph or experimental context becomes part of a complete exam answer.

Example 1: Working With Graphs

Question 1

A student wants to use a weighing scale to find the weight of her school bag.
She has a weighing scale marked in kilograms instead of newtons.
The weighing scale is not working properly.
With nothing hanging from it, the weighing scale shows 1.5 kg. The student decides to check the weighing scale.
She has no accurate weights.
Instead, she puts some tins of beans in a plastic bag and hangs it from the scale.
Her readings are shown in the table.

Number of tins of beans	0	1	2	3	4	5	6
Scale reading (in kg)	1.5	2.0	2.3	2.8	3.7	3.5	3.9

Draw a graph to show how the scale reading varies with the number of tins of
beans.

Final answer

See graph.

Mark scheme points

1. M1 Use linear scales on both axes.
2. M2 Label the axes with the quantity, scale and unit: number of tins on the horizontal axis and scale reading / kg on the vertical axis.
3. M3 Plot the seven readings accurately, to the nearest half-square. This plotting criterion is worth two marks.
4. M4 Draw a straight line of best fit through the plotted points.

Explanation

Put the independent variable, the number of tins, on the horizontal axis. Put the measured scale reading on the vertical axis and include the unit kg. The chosen scales must increase by equal amounts for equal distances.

Plot these points:

• (0, 1.5), (1, 2.0), (2, 2.3), (3, 2.8)
• (4, 3.7), (5, 3.5), (6, 3.9)

Use a single straight line of best fit, rather than joining each pair of points with separate line segments. The line should have points reasonably balanced on either side.

Common mistakes

• Using an uneven scale, such as intervals of 1, then 2, then 5 squares.
• Swapping the axes or omitting the unit kg from the scale-reading axis.
• Plotting 2.3 kg, 3.7 kg or 3.9 kg at the nearest whole number instead of at the correct position.
• Joining the points dot-to-dot or drawing a bar chart instead of using one straight line of best fit.

Example 2: Using a Diagram

Question 2

A model electric motor is used to lift a load through a vertical height.

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The load is lifted at a constant speed.

Diagram 1 shows the lifting force acting on the load as it is lifted.

Draw a labelled arrow on diagram 1 to show the other force acting on the load.

Ignore the effects of air resistance.

Final answer

Draw one vertical downward arrow labelled weight (or W or mg), equal in length to the lifting-force arrow.

Mark scheme points

1. M1 A downward arrow is labelled weight, W or mg.
2. M2 The arrow is vertically downward and equal in length to the lifting-force arrow.

Explanation

The load moves at constant speed, so its acceleration is zero and the resultant force is zero. Therefore, the force opposing the upward lifting force must act vertically downward and have the same magnitude. With air resistance ignored, this force is the load’s weight.

• Use one arrow only for the other force.
• Point it vertically downward from the load.
• Make it the same length as the upward lifting-force arrow.
• Label it “weight”, “W” or “mg”.

Common mistakes

• Do not draw the weight upwards; it acts downwards.
• Do not draw a shorter or longer downward arrow: constant speed requires equal opposing forces.
• Do not add an air-resistance arrow because air resistance is to be ignored.
• Use the technical term weight, not just “gravity” or “gravitational field strength”.
• Examiners reported that a sizable minority did not read the question fully; some drew several arrows or failed to make the downward arrow vertical and equal in length.

Practise Forces, movement, shape and momentum questions

Build a focused practice set from this part of the Edexcel IGCSE Physics syllabus.