Maximum Parallel Force of an Object

AI Thread Summary
To determine the maximum parallel force that will not set a 7.5 kg object in motion on a horizontal surface, the coefficient of static friction (us = 1.0) is used. The normal force (FN) is calculated as 73.5 N, which is the weight of the object. The maximum static friction force (Fmax) is then found by multiplying FN by us, resulting in Fmax = 73.5 N. Therefore, the maximum parallel force that keeps the object stationary is 73.5 N. The coefficient of kinetic friction is not needed for this calculation.
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"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
 
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You want to keep your object stationary, correct? So you don't even need the coefficient of kinetic friction at all.
 
well, yea, I guess I don't need the coefficient of kinetic friction.
 
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
 
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