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: Plotting a weighing-scale calibration

June 2011 · Paper 2P · Question 5(b)(i)

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

On the horizontal axis, label number of tins of beans and use a linear scale from 0 to 6, in intervals of 1. On the vertical axis, label scale reading / kg and use a linear scale from 1.0 to 4.5 kg, in intervals of 0.5 kg. Plot all the points below to within half a small square, then draw a straight line of best fit.

Coordinates (number of tins, scale reading in kg): (0, 1.5), (1, 2.0), (2, 2.3), (3, 2.8), (4, 3.7), (5, 3.5), (6, 3.9).

Mark scheme points

1. M1 Use a linear scale on each axis.
2. M2 Label both axes and show their scales; include kg for the scale-reading axis.
3. M3 Plot the seven readings at the correct coordinates, to within half a small square.
4. M4 The two plotting marks depend on plotting and scale accuracy; each plotting or scale error can lose a mark, up to two marks.
5. M5 Draw a straight line of best fit.

Explanation

The number of tins is the independent variable, so it goes on the horizontal axis. The scale reading depends on the number of tins, so it goes on the vertical axis. Equal steps on each axis must represent equal changes in value, and the scale-reading axis must show kg.

Plot every pair from the table, including the readings of 3.7 kg for 4 tins and 3.5 kg for 5 tins. The readings do not all follow a perfectly smooth trend, so use a straight line of best fit rather than joining the points one by one.

Common mistakes

• Using uneven axis intervals or leaving the scale reading without its kg unit can lose the axis mark.
• Leaving out a data point or plotting a reading at the wrong height can lose a plotting mark; check each coordinate against the table.
• Joining the plotted points one by one instead of drawing a straight line of best fit does not meet the line requirement.

Example 2: Forces on a load lifted by a motor

June 2023 (R) · Paper 1P · Question 3(b)

Question 2

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

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 arrow downwards on the load, equal in length to the lifting-force arrow, and label it weight.

Mark scheme points

1. M1 Show a downward arrow labelled “weight”, “W” or “mg” (or “gravitational force”).
2. M2 Draw the arrow vertically downwards and equal in length to the lifting-force arrow. The marks are awarded independently.

Explanation

The load travels at constant speed, so its resultant force is zero. Therefore, the downward force of the load’s weight balances the upward lifting force: the arrows must point in opposite directions and be equal in length.

Common mistakes

• Some candidates drew several arrows or added both “gravity” and “weight”; the question asks for a single labelled arrow. Draw just one arrow and label it “weight”.
• Check that the arrow is vertical and the same length as the lifting-force arrow. An arrow that is too short or not vertical may lose the second mark.
• “Gravity” alone is not the required force name for the mark; use “weight” (or an accepted label such as “W” or “mg”).

Practise Forces, movement, shape and momentum questions

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