way safety engineers build soft barriers

so that cars hitting them will slow down at a
safe rate. A person wearing a safety belt can
withstand an acceleration of 300 m/s
2
.
How thick should barriers be to safely stop
a car that hits the barriers at 81.7 km/h?
Answer in units of m

v=81.7 km/h =81700/3600=22.7 m/s

d= v²/2a=22.7²/300=1.72 m