Friction problem again Okay today is not my day

[vysis]

Homework Statement

A passennger is standing without slipping in a forward accelerating train. The coeffeciant of the feet and the floor is 0.47. Determine the maximum required acceleration of the train relative to the track if the passenger is not to slip

Homework Equations

F=ma

The Attempt at a Solution

I know that acceleration = 0, but when I rearrange the equations. I end up with
F(a) = ma + (mu)mg. But I only know (mu)... so I end up not being able to solve it.

 

[alphysicist]

Homework Statement

A passennger is standing without slipping in a forward accelerating train. The coeffeciant of the feet and the floor is 0.47. Determine the maximum required acceleration of the train relative to the track if the passenger is not to slip

Homework Equations

F=ma

The Attempt at a Solution

I know that acceleration = 0, but when I rearrange the equations. I end up with
F(a) = ma + (mu)mg. But I only know (mu)... so I end up not being able to solve it.

If you consider things from the reference frame of the ground, the man is accelerating with the same acceleration as the train. Write out Newton's law in that case. What forces are acting on him? Once you use that in Newton's law, you should find that you only have one unknown left in your equation.

 

[vysis]

but I'm not given the train's acceleration... am I missing something here =/?