Coneceptual Exercise on Static Friction

[MozAngeles]

Homework Statement

The three identical boxes shown in the figure remain at rest on a rough, horizontal surface, even though they are acted on by two different forces, F₁ and F₂. All of the forces labeled F₁ have the same magnitude; all of the forces labeled F₂are identical to one another.

Rank the boxes in order of decreasing magnitude of the force static friction between them and the surface.
Rank the boxes from highest to lowest magnitude of the force static friction between them and the surface. To rank items as equivalent, overlap them.

Homework Equations

The Attempt at a Solution

I thought it would be box 1, 3, then2 two but that it not right.

 

[kuruman]

I thought it would be box 1, 3, then2 two but that it not right.

Why makes you think that?

 

[MozAngeles]

Well the F_1 on box one is pushing in the same direction as F_2 so, it had the most net force on it.. I thought. and the box two only has F_1 pushing down on it and F_2 pushing to the right.

 

[kuruman]

Your answer is partially correct. Think in terms of horizontal components of the vector sum of F₁ and F₂ on each box. Which box has the largest total horizontal component on it? That's the box that needs the largest static friction to cancel it. Which box has the next largest horizontal component and which one has the least?

 

[MozAngeles]

thank you that helped!