Solving Friction Homework: F=ma, Fk=u*Fn

[Sarah00]

Homework Statement

Homework Equations

F = ma
Fk= u * Fn

The Attempt at a Solution

By analyzing the forces into components and applying Newton's second law

Fnet on y-axis = 0
So, Fn = mg + F2sin37 - F1sin 37 = 20 + 9 = 29 N

on x-axis
F = ma
F1 cos 37 + F2 cos 37 - Ffr = ma
F1 cos 37 + F2 cos 37 - uK * Fn = ma
5*0.8 + 20*0.8 - 0.2*29 = 2a
4 + 16 - 5.8 = 2a
14.2 = 2a
a = 7.1 m/s2Can you guide me to know my mistake, please?

Thanks in adavance

 

[TSny]

Looks like you assumed the figure depicts a side view. Maybe it's an overhead view. If so, I think you should get one of the answers listed.

 

[Sarah00]

So I find the resultant force which is:
25*0.8 - 15*0.6 = 20 i - 9j
Magnitude = 21.9 ~= 22 N

Friction force is 0.2 * 20 = 4 N

Net force = 22 - 4 = 18 N

F = ma
18 = 2a
a = 9 m/s2

thanks!

 

[TSny]

Looks good!