# Dealing with mass, acceleration and velocity

1. Sep 27, 2007

### bree

1. The problem statement, all variables and given/known data
Problem: A person wearing a seatbelt can withstand an acceleration of -0.030 m/s2. How thick should barriers be to safely stop a car that hits a barrier at 110 km/h?

2. Relevant equations
F=m*a?

3. The attempt at a solution
I so far have no attempt. I do not know what sort of formula can be used or what type of problem it is ie. constant velocity, displacement, friction so on. The sort of help that I need is a possible formula you might know of or even what kind of problem this is.

2. Sep 27, 2007

### Mentz114

I think the key formula is, with a=acceleration, v=initial speed, t=time and s=distance,

$$s = \frac{1}{2}at^2 + vt$$

Assume the barrier applies a constant deceleration.

3. Sep 30, 2007

### bree

Thank you Mentz114. That is very helpful! I'll try the problem using that formula now. Thanks again!