Torque problem - Direction and Magnitude of force exerted on socket

In summary, the problem involves determining the magnitude and direction of the force exerted by the wall socket on the bottom end of a 7-kg pole that is partially supported by a cable. The weight of a 23-kg sign suspended at the end of the pole and the angles between the pole and the vertical wall (60°) and the cable and the wall (70°) are given. The forces involved in the problem are Fcable, Fsign, Fpole, and Fsocket. The horizontal and vertical components of each force must be found and algebraic unknowns should be used for the angles.
  • #1
cdornz
40
0

Homework Statement


A 23-kg sign is suspended from the end of a 7-kg pole that is 4m long. The pole is partially supported by a cable that is attached at a point 3m up along the pole from the socket. The angle between the pole and the vertical wall is 60°, and the angle between the cable and the wall is 70°. Determine the magnitude and direction of the force exerted by the wall socket on the bottom end of the pole.

Forces in this problem would be:
Fcable, Fsign, Fpole, Fsocket
Fsign = 225.4N
Fpole = 68.6N
I don't have the force for the cable and we are trying to solve for the socket.


Homework Equations


[itex]\Sigma[/itex]Fx=0
[itex]\Sigma[/itex]Fy=0
[itex]\Sigma[/itex][itex]\Gamma[/itex]=0


The Attempt at a Solution


I know that this is a combination of a force and torque equation, but I'm not really sure how to start this problem. I have the picture from the textbook and my version of the free body diagram.
 

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  • #2
Please make some attempt at applying the equations. Find the horizontal and vertical components of each force acting on the pole. Put in algebraic unknowns where necessary (you will need one for the angle required as answer).
 
  • #3
So I've given the force equations a shot:

[itex]\Sigma[/itex]Fy=0
0=-Fcabley + Fsockety + Fpoley + Fsigny
0=-Fcablesin50° + Fsocketsin30° + 68.6sin270° + 225.4sin270°
0=-Fcablesin50° + Fsocketsin30° - 68.6 - 225.4
294 = -Fcablesin50° + Fsocketsin30°

[itex]\Sigma[/itex]Fx=0
0=-Fcablex + Fsocketx + Fpolex + Fsignx
0=-Fcablecos50° + Fsocketcos30° + 68.6cos270° + 255.4cos270°
0=-Fcablecos50° + Fsocketcos30°

Is this on the right path, I thought I was setting it up right, but I'm not sure I can get either component from the equations I made.
 
  • #4
cdornz said:
So I've given the force equations a shot:

[itex]\Sigma[/itex]Fy=0
0=-Fcabley + Fsockety + Fpoley + Fsigny
0=-Fcablesin50° + Fsocketsin30° + 68.6sin270° + 225.4sin270°
As a matter of technique, I urge you not to substitute in numbers until the very end. It's much easier to track the argument and spot mistakes if you keep it all in algebra as long as possible.
Where does sin 50 come from? I understand that's the angle between the pole and cable, but what has that to do with the vertical component of anything?
The signs don't seem consistent. Are you taking the positive y direction to be up or down?
You cannot assume the force at the socket will be along the pole. Poles are rigid so can transmit torque. The question specifically asks for the direction of that force. Put in an unknown angle for it.
 
  • #5
I've been trying to work with this for a few days and I'm seriously lost as to why my force equations aren't coming out correctly.

Fsocketx + Fsignx + Fpolex - Fcablex = 0
Fsocket + 225.4Ncos250° + 68.6Ncos270 - Fcable = 0
Fsocket = Fcablex + 77.09N

Fsockety + Fsigny + Fpoley - Fcabley = 0
Fsocket + 225.4Nsin250° + 68.6Nsin270° - Fcable = 0
Fsocket - 280.4N = Fcable

so if I were to substitute one equation into the other, then the Fsocket in both would cancel out so that doesn't really make any sense unless I'm setting up the entire force equation incorrectly.
 
  • #6
cdornz said:
Fsocketx + Fsignx + Fpolex - Fcablex = 0
Fsocket + 225.4Ncos250° + 68.6Ncos270 - Fcable = 0
Fsocket = Fcablex + 77.09N
I don't understand how you are calculating these angles.
In which direction does the weight of the sign act? What then are its horizontal and vertical components?
In which direction does the reaction from the socket act? (I answered this in a previous post.)
 

Related to Torque problem - Direction and Magnitude of force exerted on socket

What is torque and why is it important in socket problems?

Torque is a measure of the force that causes an object to rotate around an axis. It is important in socket problems because it helps determine the direction and magnitude of the force needed to turn the socket.

How do you calculate torque in a socket problem?

Torque is calculated by multiplying the force applied to the socket by the distance from the axis of rotation to the point where the force is applied. This can be represented by the equation τ = rF, where τ is torque, r is the distance, and F is the applied force.

What direction does the force need to be applied in order to loosen a socket?

The force needs to be applied in a counterclockwise direction in order to loosen a socket. This is because the direction of torque is determined by the direction of the applied force and the direction of rotation.

What factors affect the magnitude of torque in a socket problem?

The magnitude of torque is affected by the amount of force applied, the distance from the axis of rotation to the point of application, and the angle at which the force is applied. The longer the distance and the greater the force and angle, the greater the torque will be.

How can you increase the torque in a socket problem?

To increase the torque in a socket problem, you can increase the force applied, increase the distance from the axis of rotation, or change the angle at which the force is applied. You can also use a longer handle or a wrench with a higher gear ratio to increase the applied force and torque.

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