Posted by vinu on .
What is the minimum downward force on the box ( m=30 kg)that will keep it from slipping? The coefficients of static and kinetic friction between the box and the floor are 0.40 and 0.30, respectively.One person is pulling the box forward with a force of 125 N.

physics 
drwls,
The weight of the box PLUS the extra downward force F_d determines the maximum static friction force. This must balance or exceed the pulling force F_p if slipping is to be avoided.
0.40*(M g + F_d) = F_p
Solve for F_d