Physics Help Please?

Question

Can you give me an explanation with the original equations for these problems? I have a bunch more, but if these are explained to me, I'm sure I can get the rest.

1. A 3.91 kg briefcase is sitting at rest on a level floor. The acceleration of gravity is 9.81 m/s^2.
What is its acceleration (answer in units of m/s^2)?
What is its weight (Answer in units of N.)?
2. Once a 26 kg crate is in motion on a horizontal floor, a horizontal force of 52N keeps the crate moving with a constant veloctity.
The acceleration of gravity is 9.81 m/s^2.
What is the coefficient of knetic friction, between the crate and the floor?

Ok, so I realize this is my homework and i need to do it myself, so I am going to stop putting problems up, but I was looking at the rest and It would be great if someone could tell me how to find the coefficient of static friction, coefficient of kinetic friction, and how to find those if they give me degree measures to use also.

Answer 1

1.
a=0 No net force: mg=Fnormal so no a! Newton's 2nd law
F=ma=mg=3.91x9.81

2. Fnet(in the horizontal direction)=0=52N-Ffric
Ffric=Coef x Fnormal
Fnormal=mg
So: Fnet=0=52-(coef x mg) --> 52/mg=coef

Answer 2

1. The forces on the briefcase are mg down and the contact force from the floor (usually called the "normal force" or N) is up. The net force on the briefcase is zero, so the acceleration of the briefcase is zero. The weight is mg.

2. The friction force is μN where μ is the coefficient of friction. Since the crate moves with uniform velocity, the net horizontal force is zero. Therefore μN = 52 Newtons. The normal force N is equal to the weight of the crate, mg.