Coefficient of kinetic friction forces

[yoyo16]

Homework Statement

Find the applied force for a object if the coefficient of kinetic friction equals 0.30 and the acceleration equals 5m/s^2. The applied force makes a 40 degree angle with the horizontal. The mass of the object is 10kg.

Homework Equations

Fnet=ma

The Attempt at a Solution

Ff=(0.3)(10)(9.8)=29.4
(coefficient)(normal force=mg)

Fnet =Facos40-29.4
Fnet=ma
ma=Facos40-29.4
Fa=103.6

I don't know if I did this right. Can someone please explain to me how to do this correctly. Thanks!

 

[goraemon]

The Attempt at a Solution

Ff=(0.3)(10)(9.8)=29.4
(coefficient)(normal force=mg)

If I understand the question correctly, the above is not correct. That is, normal force does not equal mg in this case, rendering the rest of your calculations incorrect.

I'd start by drawing a force diagram and clearly labeling ALL the forces acting upon the object.

 

[yoyo16]

So how would you find out the friction force without knowing the normal force?

 

[goraemon]

Draw a force diagram. The problem states that the applied force makes a 40 degree angle with horizontal. Draw that force vector, along with friction force, normal force and gravitational force.

After doing so, figure out the y-component and x-component of the net Force. Start with the y-component. What are all the upward and downward forces acting upon the object?