Maximum Parallel Force of an Object

[ch3570r]

"For a 7.5 kg object on a horizontal surface that has a coefficient of static friction where us = 1.0, and a coefficient of kinetic friction where uk = 0.8, the maximum parallel force which will not set the object in motion is?"

a) 23.5 N
b) 51.2 N
c) 60.0 N
d) 73.5 N
e) 81.3 N

This is the first problem I've ever done with the coefficient of static and kinetic friction. I have these formulas; F fr = ukFN; Fmax = usFN

Im not sure if that's all I need. I do know that the Normal force (FN) is 71.8, but I am not sure how to go about finding the "max parallel force". If I solve for "Fmax" I get 71.8, but that leaves out the coefficient of static friction. I think I need help

 

[moose]

You want to keep your object stationary, correct? So you don't even need the coefficient of kinetic friction at all.

 

[ch3570r]

well, yea, I guess I don't need the coefficient of kinetic friction.

 

[ch3570r]

hold on, I was mistaken when I said 71.8 was the normal force. 7.5 * g = 73.5...which is the weight = FN. then, FN * 1 = FN, which is 73.5.

Thanks for the help moose