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### 7.4 Example 4

At what angle will start to slide a block of 3.7 kg when the coefficient of friction is 0.39?

Solution with FisicaLab

Erase the content of the chalkboard and select the SI system, and add one element Stationary reference system, one element Block above an inclined plane (to right or left), one element Force, one element Friction and one element Angles. And make the free body diagram as show the image below:

The element Stationary reference system write to default the gravity value. To the element Block above an inclined plane write the mass data. And the angle as an unknown:

m

3.7

ang

ang1

To the element Force, which represent the normal force, both entries are unknown:

f

normal

ang

ang2

And to the element Friction write the normal force and the given coefficient:

Normal

normal

u

0.39

And to the element Angles, add the two unknown angles that must be complementary:

ang1

ang1

ang2

ang2

Now click in the icon Solve to get the answer:

```
ang1 = 21.306 degrees ;  ang2 = 68.694 ;
normal = 33.816 N ;
Status = success.

```