Static Friction of sliding box on plane

[goonking]

Homework Statement

Homework Equations

Fs = μ FN

The Attempt at a Solution

Ok, so I drew a free body diagram and tilted it 90 degrees so that Fg of the small box points right and Fstatic points left.

Fg = 4.7 kg x 9.8m/s2 = 46 N

we want Fs to equal 46 N , correct? so we use the formula

Fs = (0.71) x FN

FN being the force of big box on small box

.71 x FN = 46 N

FN = 64.8N

Which is wrong. any help?

 

[ehild]

Homework Statement

Homework Equations

Fs = μ FN

The Attempt at a Solution

Ok, so I drew a free body diagram and tilted it 90 degrees so that Fg of the small box points right and Fstatic points left.

Fg = 4.7 kg x 9.8m/s2 = 46 N

we want Fs to equal 46 N , correct? so we use the formula

Fs = (0.71) x FN

FN being the force of big box on small box

.71 x FN = 46 N

FN = 64.8N

Which is wrong. any help?

You calculated the normal force between the boxes, but you need the applied force, F.

 

[billy_joule]

What is the required acceleration of box one? How is the mass of box one relevant?

 

[goonking]

You calculated the normal force between the boxes, but you need the applied force, F.

oh, silly me.

so the acceleration of the small box should be 64.8 / 4.7k which is 13.8 m/s^2

we use F=ma , m being mass of both boxes together and a being 13.8 m/s^2

F = 465 N

 

[ehild]

so the acceleration of the small box should be 64.8 / 4.7k which is 13.8 m/s^2

we use F=ma , m being mass of both boxes together and a being 13.8 m/s^2

F = 465 N

Correct!