Average G-Force Calculation for Abrupt Deceleration from 30mph in 1m Distance

[bond535]

Homework Statement

Determine the average number of g's experienced by someone abruptly coming to rest from an initial velocity of 30mph (such as in a car crash). Take the distance involved in coming to rest to be 1 m.

Homework Equations

V=Vo+at
ΔS=VoT+1/2at^2
V^2=Vo^2+2aΔS

The Attempt at a Solution

t=?
a=?
Vo= 30 mph
V=?
ΔS=?

Thank you, I'm really stuck and any help will be deeply appreciate it.

 

[lewando]

You know V_final = 0 and ΔS (change in distance) = 1m. does that help?

 

[bond535]

so...
t=?
a=?
Vo= 30 mph
V=0
ΔS=1m

V^2=Vo^2+2aΔS
0=(30mph)^2+2a(1m)
which resulted in a= -450mph

I know g= 9.8m/s ... so I'm assuming I have to change the -450mph to m/s by diving -450/3600s = 0.125m/s

I really don't know what to do next or if I'm in the right track...

 

[lewando]

V^2=Vo^2+2aΔS
0=(30mph)^2+2a(1m)
which resulted in a= -450mph

a should be in units of m/s²

(convert mph to m/s)