Static Friction of sliding box on plane

  • Thread starter goonking
  • Start date
  • #1
434
3

Homework Statement


BaQTzvR.png


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?
 

Answers and Replies

  • #2
ehild
Homework Helper
15,543
1,913

Homework Statement


BaQTzvR.png


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.
 
  • #3
billy_joule
Science Advisor
1,200
331
What is the required acceleration of box one? How is the mass of box one relevant?
 
  • #4
434
3
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
 
  • #5
ehild
Homework Helper
15,543
1,913
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!
 

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