What are the reactions at the base of the light pole in fig.1?

In summary, the problem is to determine the reactions at the base of a light pole, given the resultant force and moment caused by the weight of the pole and lamp. The solution involves finding a reaction force and moment that can balance the resultant moment, using the equation of summation of forces and moments. However, since a single force cannot balance a moment, it is necessary to find two forces or a combination of a force and a moment.
  • #1
Harmony
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Homework Statement


Determine the reactions at the base of the light pole shown in fig.1


Homework Equations


Summation of force and moment of a system in equilibrium is 0.


The Attempt at a Solution


The resultant force of due to the weight of the light pole and lamp is 185g N, vertically downward without horizontal component. The moment at the base of the light pole caused by the weight is 125g N, clockwise direction.

I realize that a reaction force at the base is needed to balance the moment, hence the reaction force will not be perpendicular to the ground. However, if that is not the case, how do you balance the horizontal component of the reaction force?

Also, if we take moment at the base, how can the reaction force contribute to the anticlockwise moment needed to counter the clockwise moment contributed by the weight?

Thanks in advanced. :)
 

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  • #2
Hi...
The problem is that the reaction for an extended body is not equivalen to a sigle force.
You need 2 forces or a force and a moment.

http://dc60.2shared.com/img/3767972/bb0c147f/forces.bmp
 
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FAQ: What are the reactions at the base of the light pole in fig.1?

1. What is the definition of equilibrium of a rigid body?

The equilibrium of a rigid body refers to a state in which the body is not moving or rotating. This means that the net force acting on the body is zero and the net torque (or rotational force) is also zero.

2. How is equilibrium of a rigid body different from equilibrium of a single particle?

In equilibrium of a single particle, the body is not moving but may still be rotating. In the case of a rigid body, both the linear and rotational motion are at rest, meaning there is no movement at all.

3. What is the significance of the center of mass in equilibrium of a rigid body?

The center of mass is a point where the entire mass of the rigid body is concentrated. In equilibrium, the center of mass remains stationary and helps us determine the forces and torques acting on the body.

4. How can we determine if a rigid body is in equilibrium?

To determine if a rigid body is in equilibrium, we must first calculate the net forces and torques acting on the body. If the net force is zero and the net torque is also zero, then the body is in equilibrium.

5. What are the conditions for static equilibrium of a rigid body?

The conditions for static equilibrium of a rigid body are that the sum of all forces acting on the body must be equal to zero and the sum of all torques acting on the body must also be equal to zero. This ensures that the body is not moving or rotating.

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