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20
p=mv.
University admission · Other / specialist pathway · Physics
Physics for the selected science pathway
Use conservation and a labelled model in physics problems.
Original Model Test for Exam unit. These questions and suggested practice times are independent Kidemy material, not an official or past paper. Choose modules for the target programme; all listed subjects are not required for every applicant.
Learn the idea
A conserved quantity must be associated with a defined system. Momentum conservation requires negligible external impulse during the interaction. Mechanical energy is not always conserved when kinetic energy transfers to thermal stores, but total energy remains accounted for.
Worked example
A 2 kg trolley at 3 m/s sticks to a stationary 1 kg trolley on a track with negligible external impulse. Final velocity = (2×3)/(2+1)=2 m/s. Kinetic energy decreases from 9 J to 6 J.
- Choose system and direction.
- Apply the conservation condition.
- Compare energy before and after.
Your written practice
Show your working on paper and enter your answer here. If it does not match, compare the model and try again.
Show model answer and explanation
6
3 kg×2 m/s=6.
Show model answer and explanation
30
P=E/t.
Write in your own words. A guardian or teacher should review this response.
Show model answer and explanation
Some kinetic energy transfers to internal energy, deformation and sound.
Account for the energy rather than saying it disappears.
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Show model answer and explanation
Otherwise external forces can change the system’s total momentum during the collision.
Connect the condition to conservation.
Physics model test
Draw a collision diagram and complete momentum and energy accounts.
Review with a guardian or teacher
- State direction and units.
- Show system boundaries.
- Distinguish total energy from kinetic energy.
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