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### 11.3 Example 3

Two blocks are joined with a string as show the image below. If the system leaves the rest, which is the acceleration of the system? Which is the velocity of each block after 0.5 seconds? The travelled distance? Solution with FisicaLab

Erase the content of the chalkboard and select the SI system. And add one element Stationary reference system, one element Block with vertical movement, one element Block with horizontal movement, and one element Relation between accelerations. And add the necessary elements Force to make the free body diagram of each block. As show the image below: To the element Stationary reference system, write:

g

9.81

t

0.5

To the block that correspond with the block above the table, we call this Block A, write:

Name

Block A

m

3

a

a_A

vi

0

vf

vf_A

d

d_A

Relative to

sf

The name is irrelevant. To its normal force write:

f

n_A

And to the force of the string:

f

t

To the other block, we call this Block B, write:

Name

Block B

m

5

a

a_B

vi

0

vf

vf_B

d

d_B

Relative to

sf

And to the force of the string:

f

t

Now, we need make a relation between the accelerations, that have the same magnitude but different sign (In the block above the table the acceleration is positive because is to the right. But in the other block the acceleration is negative because is to the downwards). We do this with the element Relation between accelerations. In this write:

a1

a_A

a2

a_B

z

-1

Now click in the icon Solve to get the answer:

```a_B = -6.131 m/s2 ;  vf_B = -3.066 m/s ;  d_B = -0.766 m ;
a_A = 6.131 m/s2 ;  t = 18.394 N ;  vf_A = 3.066 m/s ;
d_A = 0.766 m ;  n_A = 29.430 N ;
Status = success.

```

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