Question

Vehicle crumple zones are designed to absorb energy during an impact by deforming to reduce energy transfer to the occupants. How much kinetic energy, in Btu, must a crumple zone absorb to fully protect occupants in a 3000-lbm vehicle that suddenly decelerates from 10 mph to 0 mph?

Answer 1

Answer:

change in KE = -12.95 Btu

Explanation:

given data

mass = 3000-lbm

velocity of vehicle initial vi = 10 mph = 14ft/s

velocity of vehicle final vf = 0 mph = 0 ft/s

solution

as here for crumple zone to protected zone it will absorb kinetic energy

so change in KE is related here initial and final velocity that is

change in KE = 0.5 × m × (vf² - vi² ) .................1

put here value and we get

change in KE = 0.5 × 3000 × (0² - 14.7² )

change in KE = -324135 × $\frac{1lbf}{32.174\ lb.ft/s^2}$ * $\frac{1Btu}{778.17 ft.lbf}$  

change in KE = -12.95 Btu