Crash test Physics?

Question

A set of crash tests consists of running a test car moving at a speed of 12.2 m/s (26.84 m/h) into a solid wall. Strapped securely in an advanced seat belt system, a 73 kg (160.6 lbs) dummy is found to move a distance of 0.69 m from the moment the car touches the wall to the time the car is stopped. Calculate the size of the average force which acts on the dummy during that time.

Answer 1

F=m*a and
x=v0-.5*a*t^2
and v=v0-a*t

First, based on the statement,
0.69=12.2*t-.5*a*t^2
and
0=12.2-a*t
so a*t=12.2, and
0.69=12.2*t-.5*12.2*t
solve for t
t=2*0.69/12.2

with that, solve for a
a=12.2/t
or
a=12.2^2/(2*0.69)
and the force is
73*12.2^2/(2*0.69)

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Answer 2

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