IB Physics SL A.2.16 Linear momentum conservation
Build collision and recoil fluency by conserving linear momentum, finding shared speeds, and comparing how kinetic energy is split.
- Syllabus
- First assessment 2025
- Objective
- —
- Level
- SL
Exam points
- write momentum before = momentum after, with signs, to solve an unknown velocity in a collision
- for recoil, set equal and opposite momenta and use KE = p^2/2m to compare energy shares
- for sticking collisions, combine masses in the final state before solving the common speed
A.2.16—Linear momentum conservation question 1
[Maximum number: 2]
This section consists of three questions: B1, B2 and B3.
Assuming that the lithium-7 nucleus in (b) is at rest, suggest why, in terms of conservation of momentum, the neutron initiating the reaction must have an energy greater than 2.5 MeV .
2.5 MeV must be converted to mass (in the interaction) / otherwise the products would not be moving;
(to conserve momentum) final products must have total momentum equal to that of incoming neutron (so extra energy is required) / OWTTE;
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