AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Momentum is a property of moving objects: p = m v
The equation p = mv defines momentum p as the product of mass m and velocity v.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 3 of 6
Study notes
From the checked teaching notes for this specification point.
The idea
The equation p = mv defines momentum p as the product of mass m and velocity v. In this symbol equation, p is momentum in kilogram metres per second (kg m/s), m is mass in kilograms (kg) and v is velocity in metres per second (m/s). For example, a 1500 kg car travelling at 20 m/s has p = 1500 × 20 = 30,000 kg m/s. Because velocity is a vector, p is also a vector: reversing direction reverses the sign of p. A stationary object has v = 0, so p = 0. Note: Despite the tier field stating foundation and higher, this entire topic is assessed at Higher Tier only (HT only) in Combined Science.
What earns the marks
- Identify each symbol in p = mv: p is momentum, m is mass and v is velocity, with units kg m/s, kg and m/s (HT only).
- Rearrange p = mv to find mass (m = p / v) or velocity (v = p / m) when momentum is known (HT only).
- Substitute numerical values into p = mv and evaluate correctly, including standard form (HT only).
- Interpret the vector nature of p, using signs to represent opposite directions in one-dimensional problems (HT only).
Common mistakes and how to put them right
Rearranging incorrectly, for example writing m = pv.
Put it right: Use inverse operations carefully to get m = p / v (HT only).
Mixing units, such as using mass in grams with velocity in m/s.
Put it right: Convert all quantities to kg and m/s first (HT only).
Forgetting that p is a vector.
Put it right: Include direction or a negative sign when velocities are in opposite directions (HT only).
Exam tips
- Write the equation p = mv, then rearrange before substituting numbers to reduce errors (HT only).
- Include units throughout your working and check that the final unit is kg m/s (HT only).
Try the lesson
The start of the Momentum is a property of moving objects: p = m v lesson, made from checked teaching notes for this specification point.
Have a go first
A cyclist and bicycle have a total mass of 80 kg and travel at a velocity of 5 m/s. Using p = m v, what is the momentum of the cyclist and bicycle?
Listen
The equation p = mv defines momentum p as the product of mass m and velocity v. In this symbol equation, p is momentum in kilogram metres per second (kg m/s), m is mass in kilograms (kg) and v is velocity in metres per second (m/s). For example, a 1500 kg car travelling at 20 m/s has p = 1500 × 20 = 30,000 kg m/s. Because velocity is a vector, p is also a vector: reversing direction reverses the sign of p. A stationary object has v = 0, so p = 0. Note: Despite the tier field stating foundation and higher, this entire topic is assessed at Higher Tier only (HT only) in Combined Science. A strong answer earns marks for these points. Identify each symbol in p = mv: p is momentum, m is mass and v is velocity, with units kg m/s, kg and m/s (HT only). Rearrange p = mv to find mass (m = p / v) or velocity (v = p / m) when momentum is known (HT only). Substitute numerical values into p = mv and evaluate correctly, including standard form (HT only). Interpret the vector nature of p, using signs to represent opposite directions in one-dimensional problems (HT only). A common slip: Rearranging incorrectly, for example writing m = pv. Instead, Use inverse operations carefully to get m = p / v (HT only). Exam tip: Write the equation p = mv, then rearrange before substituting numbers to reduce errors (HT only).
See it
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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