🧭 Plot Summary
At 7:42 on a clear morning, a sedan hit the back of a compact stopped at a red light. Nobody saw it coming, and the sedan’s driver says she was “going about the speed limit.” What’s left is evidence: two skid marks on the road, crumpled bumpers, and a dashcam in the sedan. You are the engineer the city’s vehicle safety board has hired.
You’ll work backward through the crash in stages: the skid after the collision, the collision itself, and the skid before it. You’ll report how fast the sedan really was going, with an honest range, and check it against the dashcam. Then you’ll look at what the crash did to the two cars, find who was hit hardest and why, and recommend a real design change that would have made it safer.
What you will do in this problem
- Work backward from two skid marks and a collision to find how fast a car was going when its driver first braked.
- Report that speed as an honest range, and cross-check it against dashcam frames.
- Find how much kinetic energy the crash lost, and the force and deceleration each car’s occupants felt.
- Choose crumple-zone and bumper upgrades from a real options table, within a cost and mass budget.
- Write a memo to a vehicle safety board that defends your recommendation, and admits its limits.
Why it matters
This is the payoff for the whole unit. Momentum conservation tells you what happened in the collision, impulse and crush distance tell you what it did to the people inside, and your uncertainty habits from the Collision Lab tell you how far to trust all of it.
✅ Self-Check Before You Roll On
Check off each item as you get there. These are not grades — they are your own signal.