1. The problem statement, all variables and given/known data An object is on the dash of a car and it slides forward when the driver decelerates from 50 km/h to 0 in 3.0s or less. If the driver decelerates over a longer time it doesn't slide. What is the static coefficient? 2. Relevant equations I'm not sure. I have tried several but I feel like every equation has two unknowns. If I use v=vi + at I can get acceleration. But, then what? I don't have a mass, and it seems that I need that for F=MA, or F=mg, or to figure out Fn. 3. The attempt at a solution I've figured out the Acceleration by using v=vi + at. I can figure out the distance travelled in 3.0s by using x=x1 + Vxt + 0.5gt~2. But without mass, I don't know what else to calculate.