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8
2×(7−3)=8 N·s.
Class 9 · English Medium · Pearson Edexcel · Physics
Measurement, motion and forces
Combine impulse, momentum and the forces on an interacting pair.
Original Kidemy further-topic investigation. This optional lesson is shared by related upper pathways; select suitable depth with a teacher. It does not certify complete grade or board coverage.
Learn the idea
Impulse equals change in momentum. Equal-and-opposite interaction forces act on different bodies, so they do not cancel on one body’s force diagram. System momentum is conserved only when external impulse is negligible.
Worked example
A 0.2 kg ball changes velocity from+10 to −5 m/s. Momentum changes from+2 to −1 kg·m/s, so impulse on the ball is −3 N·s. The negative sign refers to the chosen positive direction.
- Choose system and positive direction.
- Calculate before and after momentum.
- Check external impulse and units.
Your written practice
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40
F=impulse/time.
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-2
p=mv.
Write in your own words. A guardian or teacher should review this response.
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Different masses give different accelerations under the same force magnitude.
Use F=ma and different bodies.
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The momentum change is toward the selected negative direction, not a negative amount of mass.
Connect sign to direction.
Apply the idea
Draw separate force diagrams and a system momentum account for a fictional collision.
Review with a guardian or teacher
- Use the stated evidence or givens.
- Show reasoning rather than only a result.
- Review and explain one correction.
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