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Ask iit jee aieee pet cbse icse state board community Community Discussion Question: Rotational Mechanics(Excellent Ques.)
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sachin_gupta1991 (69)

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Q. A rectangular plate ABCD of mass m and dimensions a x b is supported in
     a vertical plane by two hinges at A & B as shown in the figure. Find the instantaneous reaction of the hinge at A immediately after B is removed.
    
pannaguma (425)

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assuming AB = a and BC = b,
im getting inst acc about A as alpha = 3ag/(a^2 + b^2)^3/2

but im not able to proceed further.


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ayshwarya (285)

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WERES D PICTURE YAAAAAAAAAAAAAR
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ayshwarya (285)

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HEY PANNAGUMA IM UNABLE 2 understand how u got d acceleration yaar plz explain
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pannaguma (425)

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hey that alpha i posted is wrong.
alpha = 3ag/4*[a^2 + b^2]^1/2


and instantaneous reaction comes out
Mg/4 * [ 25 - {9b^2 / a^2 + b^2} ]^1/2


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sachin_gupta1991 (69)

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The correct answer is:
Vertical Component       (a2+4b2)mg
                                    -----------------
                                     4(a2+b2)
Horizontal  Component    3abmg
                                    -------------
                                      4(a2+b2)
 
If somebody is able to get the answer,please give me the solution.
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pannaguma (425)

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man that is what i have got, i just took the resultant.


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pannaguma (425)

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rate me.


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pannaguma (425)

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my vertical component is Mg + [3Mga^2 / 4(a^2 + b^2)]

horizontal is same.


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sachin_gupta1991 (69)

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Can u please give me  the solution
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pannaguma (425)

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ok in several parts ..............

MOI thru com for plate = M(a^2 + b^2)/12
MOI abt A = M(a^2 + b^2)/3

now find @.
T = I@
T = FL = Mg*a/2

substituting gives
@ = 3g*a/2(a^2 + b^2)

thus Acom = @R = 3ag/4*[a^2 + b^2]^1/2
since R = [(a^2 + b^2)^1/2] /2


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pannaguma (425)

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taking theta with vertical,
costheta = b/(a^2 + b^2)^1/2

sintheta = a/(a^2 + b^2)^1/2


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pannaguma (425)

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AcomX = Acom*costheta

and AcomY=Acom*sintheta

now write force eqns,
Nvetical - Mg = M*AcomY

Nhorizontal = M*AcomX

substitute and solve.

Plz rate.


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