Interactive lab · collisions & momentum
Collisions: momentum versus kinetic energy.
The costliest collision mistake is conserving the wrong quantity. This lab shows a momentum meter and a kinetic-energy meter during every collision. Momentum stays fixed; kinetic energy drops unless the collision is perfectly elastic.
- Model
- Σp constant · ΔKE ≤ 0 in impacts
- Bench
- two-cart track + conservation meters
- Practice
- 6 problem types · new numbers each time
- Feedback
- names the mistake · e.g. wrong quantity conserved
Covers sticky collisions, energy lost on impact, 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 impact: Σp stays the same, and ΣKE drops unless e = 1.
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 sticky collision
- 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 quantities are worth checking, momentum and kinetic energy, and only one is conserved here.
Practice desk 0/6 solved
Numeric answers with ±2% tolerance. Most wrong answers here come from conserving the wrong quantity, and the feedback says which one you used.
A 5 kg cart moving at 8 m/s hits a stationary 6 kg cart and they couple together. What is their common speed just after the collision?
next Next step
The energy and momentum ladder has nine problems on this choice, ending at contest level.