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kikzen
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god! this is so confusing!
P135 M2 Edexcel

6 A uniform rod AB of length 4m and mass 4 kg is freely hinged at A to a vertical wall. A force P is applied at B at right anles to the rod in order to keep the rod in equilibirum at an angle of 30 degrees to the horizontal, as shown

Find a) the magnitude of P
b) the magnitude of R, the reaction of the hinge.


hm i think ive done the first bit right;
a) taking moments about A
2(4g)(cos 30) = 4P
P = 17.0 N which is what thye get

but then b) is a total mind****.

thanks for any help
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elpaw
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you have to use both moments and newtons 1st law.
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Nylex
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(Original post by elpaw)
you have to use both moments and newtons 1st law.
1st?! You mean 3rd right?
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elpaw
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(Original post by Nylex)
1st?! You mean 3rd right?
no, 1st. i.e. all the forces will be balanced if there is an equilibrium
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Nylex
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(Original post by elpaw)
no, 1st. i.e. all the forces will be balanced if there is an equilibrium
Argh ok.
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kikzen
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(Original post by elpaw)
you have to use both moments and newtons 1st law.
yup i got that far, it was more the calculating momentst that got me.
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elpaw
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(Original post by kikzen)
god! this is so confusing!
P135 M2 Edexcel

6 A uniform rod AB of length 4m and mass 4 kg is freely hinged at A to a vertical wall. A force P is applied at B at right anles to the rod in order to keep the rod in equilibirum at an angle of 30 degrees to the horizontal, as shown

Find a) the magnitude of P
b) the magnitude of R, the reaction of the hinge.


hm i think ive done the first bit right;
a) taking moments about A
2(4g)(cos 30) = 4P
P = 17.0 N which is what thye get

but then b) is a total mind****.

thanks for any help
ok for b), if you have the reaction force as R_h (horizontal component) and R_v (vertical component)

R_h = Psin30 = 8.5N

R_v = Pcos30 - 4g = -24.47N

|R| = sqrt(R_h² + R_v²) = 25.91 N
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john !!
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Take vertical and horizontal components and solve trigonometric simultaneous equations? Draw a force diagram?
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