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Diagrama de equilíbrio de dois blocos: análise individual e global, Exercícios de Engenharia Elétrica

Neste documento, é apresentado o análise de equilíbrio de dois blocos que interagem entre si, utilizando-se diagrama de corpo livre. A força de contato (f′) e a força de fricção estática (fs) são consideradas, sendo a força de fricção máxima (fs,max) determinada pela coeficiente de fricção (µs). A análise é feita primeiro para cada bloco individualmente e depois combinada para o sistema completo, que se desloca sobre um piso sem fricção. As expressões para a aceleração e as forças resultantes são derivadas a partir da segunda lei de newton.

Tipologia: Exercícios

Antes de 2010

Compartilhado em 08/10/2007

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25. The free-body diagrams for the two blocks, treated individually, are shown below (first mand then M).
Fis the contact force between the two blocks, and the static friction force
fsis at its maximum value
(so Eq. 6-1 leads to fs=fs,max =µsFwhere µs=0.38).
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F
F
mg
fs
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N
Mg
F
Treating the two blocks together as a single system (sliding across a frictionless floor), we apply Newton’s
second law (with +xrightward) to find an expression for the acceleration.
F=mtotal a=a=F
m+M
This is equivalent to having analyzed the two blocks individually and then combined their equations.
Now, when we analyze the small block individually, we apply Newton’s second law to the xand yaxes,
substitute in the above expression for a, and use Eq. 6-1.
FF=ma =F=FmF
m+M
fsmg =0 =µsFmg =0
These expressions are combined (to eliminate F) and we arrive at
F=mg
µs1m
m+M
which we find to be F=4.9×102N.

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25. The free-body diagrams for the two blocks, treated individually, are shown below (first m and then M ).

F

is the contact force between the two blocks, and the static friction force

f

s

is at its maximum value

(so Eq. 6-1 leads to f

s

= f

s,max

s

F

where μ

s

F

F

mg

f

s

N

Mg

F

Treating the two blocks together as a single system (sliding across a frictionless floor), we apply Newton’s

second law (with +x rightward) to find an expression for the acceleration.

F = m

total

a =⇒ a =

F

m + M

This is equivalent to having analyzed the two blocks individually and then combined their equations.

Now, when we analyze the small block individually, we apply Newton’s second law to the x and y axes,

substitute in the above expression for a, and use Eq. 6-1.

F − F

= ma =⇒ F

= F − m

F

m + M

f

s

− mg = 0 =⇒ μ

s

F

− mg = 0

These expressions are combined (to eliminate F

) and we arrive at

F =

mg

s

m

m+M

which we find to be F = 4. 9 × 10

N.