Static friction and kinetic friction

[Revolver]

Another concept my physics prof didn't teach the class. I would love to be able to attempt these problems but I have no idea what these concepts are or the formulas for them. I'm not looking for the answers to these problems here folks, but rather a method in which to solve them. Thanks!

1. A 750 N box moves at a constant velocity on a floor with a coeficient of static friciton of .800 and a coefficient of kinetic friction = .600. What is the horizontal force required to keep the box moving?

All I can think to do here is draw a diagram with vectors, but I honestly have no idea what to do.

2. A 750 N box rests on hte floor with a coefficient of static friction = .800 and a coefficient kinetic friciton of 0.600. What is the force of friction if a horizontal force of 550 N is applied to the box?

Again, no idea.

3. In order to slide a 70.0 kg box across the floor at a constant speed, you must push horizontally with a force of 351 N. What is the coefficient of kinetic friciton?

 

[russ_watters]

Drawing a diagram would be a good start...

 

[Revolver]

I did.. thing is I don't know the formulas, or the method to solve it. I'm not looking for the answer, but rather for someone to explain how to tackle these problems. Thanks.

 

[Revolver]

Anybody know the formula?

 

[Hootenanny]

A rather useful thread by Doc Al can be found https://www.physicsforums.com/showthread.php?p=920984#post920984" may be of particular interest to you.

 

[hakojackie]

The formula you want is Fmax=Us*Fn where Fs is what you are trying to find and Us (meu) is the coefficient of static friction and Fn is normal force