Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Describe examples of momentum in collisions
Full specification wording
Topic 2 – Motion and forces: 2.25 Describe examples of momentum in collisions
Momentum is mass × velocity, so a moving object carries momentum in the direction it travels.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 24 of 32
Study notes
From the checked teaching notes for this specification point.
The idea
Momentum is mass × velocity, so a moving object carries momentum in the direction it travels. In a collision, momentum is conserved when no external resultant force acts: the total momentum before equals the total momentum after. Describe examples by naming the objects, giving their masses and velocities, and comparing total momentum before and after. For instance, a 2 kg trolley moving at 3 m/s has momentum 6 kg m/s; if it collides with a stationary 1 kg trolley and they stick together, the combined 3 kg mass moves at 2 m/s, giving 6 kg m/s again. A rocket expelling gas backwards is a recoil example, not a collision.
What earns the marks
- States that momentum equals mass multiplied by velocity and is a vector quantity with direction.
- Identifies the objects involved in a collision and gives their masses and velocities before impact.
- Calculates total momentum before the collision by summing the individual momenta with correct signs.
- Compares total momentum before and after the collision to show it is conserved when no external resultant force acts.
- Describes a recoil or explosion example, such as a rocket or two separating trolleys, where total momentum stays zero.
Common mistakes and how to put them right
Adds momenta without regard to direction.
Put it right: Assign opposite directions opposite signs before summing.
Treats momentum as a scalar and ignores velocity direction.
Put it right: State that momentum is a vector.
Assumes momentum is lost in every collision.
Put it right: Distinguish elastic and inelastic collisions, where momentum is conserved but kinetic energy may not be.
Confuses momentum with kinetic energy.
Put it right: Keep mass × velocity separate from ½mv².
Exam tips
- Write the momentum equation and substitute values with units before choosing an option.
- Check the direction of each velocity and use signs consistently in the total.
- Eliminate options that ignore conservation of momentum when no external force acts.
- Show the before-and-after totals so the reasoning is visible.
Try the lesson
The start of the Topic 2 – Motion and forces: 2.25 Describe examples of momentum in collisions lesson, made from checked teaching notes for this specification point.
Have a go first
Why does a moving car have more momentum than a bicycle moving at the same speed?
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Topic 2 – Motion and forces: 2.25 Describe examples of momentum in collisions
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge