1. , =20 , , . 10 . 30. α, , N .
_
_ _ Q
Q N
α α
α 60 β
_ _
A _ A P N
P 30o
30o
г. , . 䳺 ( ), , . , . Q, , . (P,N,Q)~0 .
, , , N , Q . , N, , , Q, N, . .
N, α β, .
(P/sinβ)=(N/sinα)=(Q/sin30o)
sinβ=(P*sin30o/Q)=1; β=90
α=180-90 -30=60
N=(P*sinα/Q)=17,32 ()
³ N=17,32; α=60o
2. , . 䳺 =5 45 . , . .
D
y
_ _ _
RA P RB
A α 45o
C B x
1 3
_ _ _ _ _
г. 䳺 RA, P, RB. . , . , .
.
D, 璺 A D, . RA α. , , ((, , )~0).
+ + =0
. β=180-(45+45-α)=90+α
_
45o RB
_ β
P
_
45o-α RA
α
(P/sinβ)=(RB/sin(45-α))=(RA/sin45o), RA=(sin45o/ sin(90-α))*
RA=(sin45o/ cosα)*; RB=(sin(45o-α) /cosα)*=(sin45o- cos45o*tgα)*P
cosα, tgα.
=4; BD=3, AD=5
cosα=(AB/AD)=4/5=0,8; tgα=(BD/AB)=3/4=0,75
RA= (sin45o/cosα)*P=4,42 (kH)
RB=(sin45o- cos45o* tgα)*P=0,88 (kH)
³: RA= 4,42 kH, RB=0,88 kH
1 2 - . 2, , .
|
|
. , y.
ΣPkx=0; -Pcos45o+PAcosα=0
ΣPky=0; RAsinα-Psin45o+ RB =0
RA=*(cos45o/cosα)=(sin45o/cosα)*P (cos45o=sin45o)
RB=Psin45o-RAsinα = Psin45o-P*sinα*(cos45o/cosα)
RB=P(sin45o-cos45o*tgα)