Physics Friction: Find Coefficient of Friction

[xCrissyX]

Homework Statement

While dragging your 22.3 kg catapult across the floor of your garage, you wonder what coefficient of friction is between the catapult and the concrete. If you accelerate your catapult at 0.76 m/s2 with a force of 79 N at 21°, find:

1. Find the components.
Fx=
Fy=
2. Force Normal: FN =
3. What is the coefficient of friction (mu/μ) between the dry concrete and the wood of your catapult? μ=

Homework Equations

where Vf= final velocity Vi= initial velocity a= acceleration t= time

x= distance in the x direction (can also be replaced with y in the y direction)

Fnet= ma (Net force= mass times acceleration)

Ff= μ FN (Force of friction= mu[coefficient of friction] times Normal Force)
3. The Attempt at a Solution
I have figured out the first three questions correctly;
Fx= 73.8N using mgcos(theta) (theta is the degree of the incline)
Fy=28.3N using mgsin(theta) (x and y the postions on a graph)
Force Normal= 190.2N using Fnormal+Fgravity+Fpull (sin theta)=0

I can't figure out how to find the mu between the concrete and the wood, I got 4.67 as my answer but the problem is telling me the correct answer is .2968. I know Ffriction is needed but I'm not sure if I'm doing it correctly, since I was not given any equation for it. After finding that I would think just plugging that into the last equation to find mu?

 

[ehild]

Homework Statement

While dragging your 22.3 kg catapult across the floor of your garage, you wonder what coefficient of friction is between the catapult and the concrete. If you accelerate your catapult at 0.76 m/s2 with a force of 79 N at 21°, find:

1. Find the components.
Fx=
Fy=
2. Force Normal: FN =
3. What is the coefficient of friction (mu/μ) between the dry concrete and the wood of your catapult? μ=
Fnet= ma (Net force= mass times acceleration)

Ff= μ FN (Force of friction= mu[coefficient of friction] times Normal Force)
3. The Attempt at a Solution
I have figured out the first three questions correctly;
Fx= 73.8N using mgcos(theta) (theta is the degree of the incline)
Fy=28.3N using mgsin(theta) (x and y the postions on a graph)
Force Normal= 190.2N using Fnormal+Fgravity+Fpull (sin theta)=0

There is no incline, the floor is horizontal. But you apply a force F which makes the angle of 21°with the horizontal. Fx and Fy are the horizontal and vertical components of your force. Apart of these, the results are correct.

I can't figure out how to find the mu between the concrete and the wood, I got 4.67 as my answer but the problem is telling me the correct answer is .2968. I know Ffriction is needed but I'm not sure if I'm doing it correctly, since I was not given any equation for it. After finding that I would think just plugging that into the last equation to find mu?

Show your work in detail. What is the net horizontal force applied on the catapult?