# Car stopping on a dime

1. Feb 2, 2012

### Loren Booda

What is the g-force on a car, initially traveling at 55 mph, when stopping across the diameter of a dime?

2. Feb 3, 2012

### Pythagorean

convert mph to mps, find the acceleration from change in velocity, multiply by mass, divide by g.

3. Feb 3, 2012

### Pythagorean

Find acceleration from change in velocity over given distance, that is.

4. Feb 3, 2012

### KingNothing

Would it not be appropriate to solve a system of equations, d=1/2 * a * t^2, d = 17.91 mm, and a * t = 55 mph?

Doing this I get about 16.9 kilometers / s^2, or 1721g.

Last edited: Feb 3, 2012
5. Feb 3, 2012

### Pythagorean

$$a = \frac{v^2 - v_0^2}{2d}$$

but $$v_0 = 0$$ (in my ref frame : )

so

$$a = \frac{v^2}{2d}$$

Of course, this assume constant acceleration...