Evaluate Collision Design Solutions Practice Test

A helmet prototype spreads impact force over different contact areas to reduce pressure on the skull. Two designs produce the same average impact force $F_{\text{avg}}=3000,\text{N}$, but have different contact areas.

Design A: contact area $A=30,\text{cm}^2$

Design B: contact area $A=60,\text{cm}^2$

Design C: contact area $A=90,\text{cm}^2$

Safety criterion: keep average pressure below $P_{\max}=50,\text{kPa}$. Use $P=F/A$ and convert areas: $1,\text{cm}^2=1\times 10^{-4},\text{m}^2$.

Which design(s) meet the pressure limit?

An automotive engineer compares restraint designs using impulse. A 60 kg passenger moves forward at 15 m/s relative to the car just before the restraint engages and is brought to rest. The maximum allowable average force on the passenger is 5000 N.

Design A: standard seatbelt, $\Delta t=0.080,\text{s}$

Design B: seatbelt with pretensioner + load limiter, $\Delta t=0.120,\text{s}$

Design C: seatbelt + airbag, $\Delta t=0.200,\text{s}$

Which design(s) keep $F_{\text{avg}}=\Delta p/\Delta t$ below 5000 N?