9.11 Example 11

A uniform block of 25 kg and 50 cm of edge, as show the image below, is placed on a slope of 20 degrees. If we want move up the block as fast as possible (constant speed) by the horizontal force F, What is the maximum possible coefficient of friction? Which is the force?

Solution with FisicaLab

Select the group Static and, inside this, the module Static of solids. Erase the content of the chalkboard and select the SI system. And add one element Stationary reference system, one element Solid, two elements of solid and the necessary elements Force and Friction, as show the image below:

The Stationary reference system set the gravity value to default. Now to the element Solid, that we call Block we have:

Name

Block

m

25

xc

25 @ cm

yc

25 @ cm

ang

20

To the element of solid that represent the upper corner, where is applied the force F, we have:

Name

Block

x

0

y

50 @ cm

And to the horizontal force:

f

F

The normal force and the friction are applied to the element of solid that represent the lower right corner. Because when we move up the block as fast as possible, the tipping is imminent. Then, we have:

Name

Block

x

50 @ cm

y

0

To the force that represent the normal force:

f

N

ang

70

And to the friction:

Normal

N

ang

20

u

u

Now click in the icon Solve to get the answer:

F = 262.970 N ;  N = 320.401 N ;  u = 0.509 ad ;
Status = success.