Interactive lab · collisions & momentum
Two ledgers, one impact — only one survives.
The most expensive collision mistake isn't arithmetic — it's conserving the wrong quantity. This bench keeps a momentum meter and a kinetic-energy meter running through every impact, so you can watch one hold perfectly still while the other collapses.
- Model
- Σp constant · ΔKE ≤ 0 in impacts
- Bench
- two-cart track + conservation meters
- Practice
- 6 problem types · randomized values
- Feedback
- trap-matched · names the wrong ledger
Objectives: sticky-collision speed, energy lost to coupling, recoil, and the two-stage ballistic pendulum.
conserved through every impact
survives impact only if e = 1
- v₁
- 8 m/s
- v₂
- 0 m/s
- predicted v₁′
- 3 m/s
- predicted v₂′
- 3 m/s
- KE lost
- 60 J
- p check
- 24 = 24
Watch the two meters at the moment of impact: Σp never moves, ΣKE drops unless e = 1. Choosing which ledger to trust — that's the entire skill this lab trains.
Predict first then test it
Two identical carts on a frictionless track. Cart A moves right at 6 m/s; cart B is at rest. They collide perfectly elastically. What happens?
Worked example two ledgers, one impact
- 01
Model
A 4 kg cart at 6 m/s couples with a stationary 8 kg cart on a frictionless track. We want the final speed and the kinetic energy lost. Two ledgers are in play — momentum and kinetic energy — and only one survives the impact.
Practice desk 0/6 solved
Numeric answers with ±2% tolerance. Every wrong path here is a conservation-law choice — answer with the wrong ledger and the feedback will say so by name.
A 3 kg cart moving at 8 m/s hits a stationary 8 kg cart and they couple together. What is their common speed just after the collision?
next Pressure-test the model
The energy–momentum ladder runs this exact decision through nine rungs, ending at contest level.