Solving for friction with only acceleration

[wmdavid]

Homework Statement

You are on a train accelerating at .2g; what is the minimum coefficient of static friction that your shoes have to have with the base of the train in order to not move?

You are only given the acceleration of the train. Not your mass or the natural force.

Homework Equations

F=MA, F= mew * natural force

The Attempt at a Solution

I have tried approaching it from several diffrent angles, looking it as F=MA and F= mew * natural force, but with only the acceleration, I do not see a way to solve the problem. Their are just too many variables. If I knew the mass of the person, I could easily solve it, by dividing the force by the natural force, but you aren't givin that.

 

[Doc Al]

What you call 'natural force' should be the normal force. You don't need the actual mass--just call it 'm' and see what happens. How do you calculate the normal force in this situation?