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### 7.3 Example 3

A block, with a mass of 3 kg, is maintained against the wall, to a horizontal force F. If the friction coefficient between the block and wall is 0.25, which is the minimal force F, to avoid the fallen of the block? Solution with FisicaLab

The minimal force F, correspond to the case when the friction force is maximum. With this in mind, erase the content of the chalkboard ans select the SI system, and add two elements Horizontal force, one element Friction, one element Block and one element Stationary reference system, to make the free body diagram of the block. As show the image below: To the Stationary reference system:

g

9.81

To the element Block, write:

m

3

To the element Horizontal force that correspond to the force F, write:

f

F

Because is an unknown data. To the element Horizontal force that correspond to the normal force, write:

f

n

Is an unknown data too. Now, to the element Friction write:

Normal

n

u

0.25

Now click in the icon Solve to get the answer.

```F = 117.720 N ;  n = 117.720 N ;
Status = success.

```