A man is pulling two suitcases, one on top of the other. Bottom case mass=25kg and top mass = 15kg. The coefficient of friction between the two cases and between the bottom case and the floor can both be represented by Uk = .4 and Us =.5. Find the maximum acceleration of the cases so they move with respect to the floor, but not with respect to one another.
The Attempt at a Solution
Fs = un for the two boxes.
Fs = .5*15
Fs = 7.5N.
This means exceeding 7.5N of force will cause the boxes to accelerate with one another. Now I need to plug this value into another equation such that I find the maximum acceleration of the two boxes. Using F=ma setting F equal to 7.5 does not work, as this gives an extremely tiny acceleration. I think another F=un is needed, but im not sure how to set the second one up in a way that allows me to use the 7.5N I figured out before.