# Automobile collision-speed passenger crashes against dashboard

1. Sep 14, 2009

### physicsquest

1. The problem statement, all variables and given/known data
In a collision, an automobile initially traveling at 50 km/h decelerates at a constant rate of 200 m/s^2. A passenger not wearing a seat belt crashes against the dashboard. Before the collision, the distance between the passenger and the dashboard was 0.60 m. With what speed, relative to the automobile, does the passenger crash into the dashboard? Assume that the passenger has no deceleration before contact with the dashboard.

initial velocity: 50 km/h= 13.89 m/s
a= -200 m/s^2
x-x0= 0.60 m

2. Relevant equations
x-x0= 1/2(v0+v)t
a= (v^2-vo^2)/2(x-x0)

3. The attempt at a solution
-200 m/s^2= (v^2-179.29 m^2/s^2)/1.2 m

answer is supposed to be 15.5 m/s.

2. Sep 15, 2009

### Dick

The question asks for the velocity relative to the automobile. The initial velocity of the passenger relative to the automobile is 0m/sec. Try working it that way.