Can't Derive Friction From Equation

[interXdragon]

A question that I've spent hours on, but still can't seem to extract friction from it:

10.) A flight attendant pulls her 70.0N flight bag a distance of 253m along a level airport floor a a constant velocity. The force she exerts is 40.0N an angle of 52.0 Degrees horizontal. Find the following

b. the work done by force of friction on the flight bag​

c. the coefficient of kenetic friction between the flight bag and the floor​

Any suggestions?

 

[siddharth]

What have you done till now?

 

[interXdragon]

I've figured out A... which asks for the work done by the flight attendant. I've looked up the three friction equations. I've tried solving C by using mu = fmax/fnormal ( mu = 40N / 70N ). And I've put a lot of thought into the two other equations, but they solve for the cofficient itself, which isn't the question.

 

[siddharth]

Have you drawn the FBD for the bag and split the components of the force? Also, since the velocity is constant, what can you say about the net sum of the forces along the horizontal direction?

 

[interXdragon]

Yes, I always draw a picture for my hardest questions. At the moment, I don't have a camera to take a picture of my work, however, I've created a little picture that imitates the work on my paper. Here it goes:
http://unityofthedragons.org/ex.jpg

This doens't include my answers because I kinda rushed to do this picture. However, the idea is there. Thanks a lot for helping please correct me if I'm wrong.

 

[siddharth]

You should include all the forces in your FBD. That includes the normal force from the ground and the force due to friction. Can you post and show the equations you get?

 

[interXdragon]

yes, please give me sometime

 

[interXdragon]

Okay, here you go, this includes the friction equations:

http://unityofthedragons.org/ex.jpg

 

[siddharth]

Why does static friction come into play here? The block is moving, so only kinetic friction will exist. And that will be $$\mu_k N$$.
The value of the Normal force is not $$mg$$.
You should write the components of the 40 N force along the horizontal and vertical direction. Once you do that, you can calculate the normal force.

 

[interXdragon]

I understand now, thanks for all your help, siddharth!