physics
posted by norm .
Posted by norm on Monday, March 15, 2010 at 9:21am.
What is the minimum downward force on the box in the figure that will keep it from slipping? The coefficients of static and kinetic friction between the box and the floor are 0.30 and 0.20, respectively. Box weighs 30 kg with 125 newtons pulling on horizontal surface.

The required friction force will depend upon the static coefficient. The required downward force Fy to make the friction force equal the pulling force Fx is given by
(Fy + Mg)*0.30 = Fx
Solve for Fy. M = 30 kg and Fx = 125 N
The kinetic friction coefficient is not needed.