physics homework?

Question

A car traveling at 56 km/h hits a bridge abutment. A passenger in the car moves forward a distance of 69 cm (with respect to the road) while being brought to rest by an inflated air bag. What magnitude of force (assumed constant) acts on the passenger's upper torso, which has a mass of 31 kg?

just help with the equation for it, im trying to find the time taken but i dunno wat equation. well i think if i get hte time then il get the question right lol.

thanks for the help

Answer 1

I think you have to assume a constant acceleration a. There are two equations you can set up for this condition:

The acceleration a = ∆v/t

The distance traveled under acceleration a is s=.5*a*t^2;

from the first, t = ∆v/a, put this in the second s = .5*a*∆v^2/a^2= .5*∆v^2/a. Solve for a (s you know is 69cm).

now you can get a from a = .5*∆v^2/s; (the ∆v in this case is 56 km/h). Once you have a, the force is F= m*a.

Be careful since you have mixed units here.

Answer 2

simplest way to solve
work done =change in kinetic energy
f*x=1/2mv^2
f=mv^2/(2x) v=56km/hr=.....m/s
m=31kg
x=69/100 m
just use it and you will get your answer

Answer 3

I withdraw my answer for further thought