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Equilibragem de Forças em um Sistema Dinâmico: Blocos e Nó, Exercícios de Engenharia Elétrica

O diagrama de corpo livre para bloco b e para o nó acima de a. Os tensões forças t1 e t2, a força de fricção estática f, a força normal n, o peso de a (wa) e o peso de b (wb) são considerados. Aplicando a lei de newton em direções x e y para o bloco b e depois fazendo a mesma coisa para o nó resultam em quatro equações. Solução destas equações com µs = 0,25 fornece wa ≈ 100 n.

Tipologia: Exercícios

Antes de 2010

Compartilhado em 08/10/2007

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19. The free-body diagrams for block Band for the knot just above block Aare shown below.
T1is the
tension force of the rope pulling on block Bor pulling on the knot (as the case may be),
T2is the tension force exerted
by the second rope (at angle
θ=30
)ontheknot,
fis the
force of static friction exerted
by the horizontal surface on
block B,
Nis normal force ex-
ertedbythesurfaceonblock
B,WAis the weight of block
A(WAis the magnitude of
mAg), and WBis the weight
of block B(WB= 711 N is
the magnitude of mBg).
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T1
f
mBg
N
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T2
T1
mAg
θ
For each object we take +xhorizontally rightward and +yupward. Applying Newton’s second law in
the xand ydirections for block Band then doing the same for the knot results in four equations:
T1fs,max =0
NWB=0
T2cos θT1=0
T2sin θWA=0
where we assume the static friction to be at its maximum value (permitting us to use Eq. 6-1). Solving
these equations with µs=0.25, we obtain WA= 103 100 N.

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19. The free-body diagrams for block B and for the knot just above block A are shown below.

T

is the

tension force of the rope pulling on block B or pulling on the knot (as the case may be),

T

is the tension force exerted

by the second rope (at angle

) on the knot,

f is the

force of static friction exerted

by the horizontal surface on

block B,

N is normal force ex-

erted by the surface on block

B, W

A

is the weight of block

A (W

A

is the magnitude of

m

A

g), and W

B

is the weight

of block B (W

B

= 711 N is

the magnitude of m

B

g).

T

f

m

B

g

N

T

T

m

A

g

For each object we take +x horizontally rightward and +y upward. Applying Newton’s second law in

the x and y directions for block B and then doing the same for the knot results in four equations:

T

− f

s,max

N − W

B

T

cos θ − T

T

sin θ − W

A

where we assume the static friction to be at its maximum value (permitting us to use Eq. 6-1). Solving

these equations with μ

s

= 0.25, we obtain W

A

= 103 ≈ 100 N.