lesson
Conservation applies to a defined system
1 · Learn
Momentum is mass times velocity and has direction. In a closed system with no resultant external force, total momentum is conserved during an interaction. Internal forces can change individual momenta while the system total remains constant.
Choose a positive direction and include every relevant object. Kinetic energy need not be conserved in an inelastic collision even when momentum is conserved.
2 · Worked example
A 2 kg object moving at 3 m/s has momentum 6 kg m/s. If it joins a stationary 1 kg object in an ideal isolated collision, the combined 3 kg moves at 2 m/s.
3 · Your turn
In that example, what total momentum exists after the objects join?
Check your answer
6 kg m/s in the original direction.
4 · Apply your learning
Compare momentum before and after using a paper model and distinguish the separate kinetic-energy calculation.
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Check a calculation · Year 5 onward
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Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
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