| Difficulty | Secondary School | High school/other |
| ★ | Basic | Easy |
| ★★ | Demanding | Basic |
| ★★★ | Demanding | |
| ★★★★ | Difficult | |
| ★★★★★ | Very difficult |
Determine the mass of the second wagon (wagon with a spring at the end). How much of kinetic energy is converted into thermal energy in a collision (percentage)?
Answer: 530 g, 28 %