Hi, we're starting our chapter on Newton's Laws and force and I wanted to know if I am approaching the following problem correctly: A car travels 53 km/h and hits a bridge abutment (what's that?). The person in the car moves forward 65 cm (w/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 41 kg? Well, I believe that the Vo of the car will also be the Vo of the person. So: Voc = Vop = Vo = 53 km/h = 14.72 m/s The distannce the person moved forward: Dp = X-Xo = 65 cm = 0.65 m Because the airbag brought the person to rest: Vf = 0 m/s We now have Vo, X-Xo, and Vf. We can find a: V^2 = Vo^2 + 2a(X-Xo) --> a = -166.676 m/s^2 Using F=ma: F = ma = (41)(-166.676) = -6833.7 N Because they are looking for magnitude, I can take the abs value of F and get my answer: 6.8 x 10^3 N Was my approach correct? Is F negative because a was negative, meaning it was decelerating?