Rotational Equilibrium: Finding Force at Point B and D

AI Thread Summary
The discussion revolves around solving a problem related to rotational equilibrium, where the net torque must equal zero. The participant calculates the torque caused by a 10N force, which creates a clockwise torque, while questioning the effects of forces at points B and D. It is clarified that the force at point B will indeed cause counterclockwise torque, and the lever arm for point D is confirmed to be 0.04m. The participant concludes that their calculations lead to a force of 7.5N at point D, confirming their reasoning as correct. The exchange emphasizes understanding torque direction and the application of forces in rotational systems.
reder
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Hello I've attached the problem. Any help would be greatly appreciated.



I understand that by giving us the clue of rotational equilibrium, it means net T has to be 0. The force at 10N will cause clockwise torque (T= rF, so T = .04m * 10N). The thing that confuses me is the force at point B, will it cause counterwise torque or no torque? Also I know the force that we are finding at point D will give us counterclockwise torque, but is the moment arm or lever arm going to be .04m too?

Thank You.
 

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Hi reder! Welcome to PF! :smile:

reder said:
I understand that by giving us the clue of rotational equilibrium, it means net T has to be 0.

You're right there!

The thing that confuses me is the force at point B, will it cause counterwise torque or no torque?
Think about a situation of such a hinged block, and you applying adequate force to it at the lower end(B). Would it rotate? If yes, which way?

but is the moment arm or lever arm going to be .04m too?
By definition, torque about a point is the force multiplied by the perpendicular distance between the line of action of force and the point. What does that tell you about the lever arm length? :wink:
 


Think about a situation of such a hinged block, and you applying adequate force to it at the lower end(B). Would it rotate? If yes, which way?
My guess would be, it would rotate counterclockwise.

By definition, torque about a point is the force multiplied by the perpendicular distance between the line of action of force and the point. What does that tell you about the lever arm length? :wink:[/QUOTE]
So I can just extend the line of action of force at point D and this in turn would make it the lever arm .04m.

So if I am taking clockwise as negative torque and counterclockwise as positive torque... - -.04(10N) + (5N) (.02) + (F) (.04)= 0
.4 = .1+ .04F
F = 7.5N...(Is my reasoning correct)...
Also thanks for a quick reply...
 


reder said:
My guess would be, it would rotate counterclockwise.

Right-o!


So if I am taking clockwise as negative torque and counterclockwise as positive torque... - -.04(10N) + (5N) (.02) + (F) (.04)= 0
.4 = .1+ .04F
F = 7.5N...(Is my reasoning correct)...

Absolutely.
 


Thx infinitum for the help...
 

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