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Help moments q physics please

C ? (ms=0.7)
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Reply 1
Avatar for Batman2k1
Batman2k1
OP
14
b) beam falls why?
a c is obvious clockwise overall

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Reply 2
Avatar for sh.hr
sh.hr
8
the mobile is in equilibrium so the moment on the left hand side equals the moment on the right hand side. objects A and B are the same distance from the pivot on their side and their moments equal one another (rods are horizontal), hence their weight must be the same, as you have written. M=F⋅dM=F \cdot d, and MLHS=MRHS=0.8⋅0.1=0.08NmM_{LHS}=M_{RHS}=0.8 \cdot 0.1=0.08Nm. We can calculate the force acting on the RHS as F=Md=0.080.1=0.8NF=\frac{M}{d}=\frac{0.08}{0.1}=0.8N. Hence the weight of C must be WC=0.8−WD=0.8−0.1=0.7NW_{C}=0.8-W_{D}=0.8-0.1=0.7N
Reply 3
Avatar for sh.hr
sh.hr
8
the rod supporting C and D falls because the rod supporting it rotates clockwise, bringing the rod closer to the ground. It will, however, still stay horizontal (ignoring other forces).
Reply 4
Avatar for Batman2k1
Batman2k1
OP
14
OMG, thank you so much.
Damn, how did i not notice that, gotta consider the system component as a whole.
Original post by sh.hr
the mobile is in equilibrium so the moment on the left hand side equals the moment on the right hand side. objects A and B are the same distance from the pivot on their side and their moments equal one another (rods are horizontal), hence their weight must be the same, as you have written. M=F⋅dM=F \cdot d, and MLHS=MRHS=0.8⋅0.1=0.08NmM_{LHS}=M_{RHS}=0.8 \cdot 0.1=0.08Nm. We can calculate the force acting on the RHS as F=Md=0.080.1=0.8NF=\frac{M}{d}=\frac{0.08}{0.1}=0.8N. Hence the weight of C must be WC=0.8−WD=0.8−0.1=0.7NW_{C}=0.8-W_{D}=0.8-0.1=0.7N
Reply 5
Avatar for Batman2k1
Batman2k1
OP
14
ohhh okay, turngn effect of force of course.
i needed to confirm that thanks.

Interesting it remains horizontal? I guess because the moments acting on the bar are still balanced.

or that the tension and the distances of the wire remain the same?
If the tension was significantly less, then i think it will turn - hmmm i had seen a question of this with an orchment but, it was saying why does it stay horizontal?

Does that make sense - i wonder why that is if u know this
Original post by sh.hr
the rod supporting C and D falls because the rod supporting it rotates clockwise, bringing the rod closer to the ground. It will, however, still stay horizontal (ignoring other forces).
Reply 6
Avatar for sh.hr
sh.hr
8
Original post by Batman2k1
ohhh okay, turngn effect of force of course.
i needed to confirm that thanks.

Interesting it remains horizontal? I guess because the moments acting on the bar are still balanced.

or that the tension and the distances of the wire remain the same?
If the tension was significantly less, then i think it will turn - hmmm i had seen a question of this with an orchment but, it was saying why does it stay horizontal?

Does that make sense - i wonder why that is if u know this

Considering that the rod will accelerate towards the ground as the top rod lowers it, the tension in the wire will change but this shouldn't affect the orientation (assuming that the force is uniform along the wire)
Reply 7
Avatar for Batman2k1
Batman2k1
OP
14
The tension changes because T= ma +mg takes effect because, when a mass of an object accelerates from rest, there is a force, and this is corresponds with newtons 2nd law?
Tension is not looser but stiffer as the forces must balance as everything does in physics. Why?
So bar remains horizontal due to forces not changing the orientation as it is balanced again.


Original post by sh.hr
Considering that the rod will accelerate towards the ground as the top rod lowers it, the tension in the wire will change but this shouldn't affect the orientation (assuming that the force is uniform along the wire)

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