# Homework Help: Equilibrium of Rigid Body

1. Aug 12, 2008

### Harmony

1. The problem statement, all variables and given/known data
Determine the reactions at the base of the light pole shown in fig.1

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

3. 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 realise 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?

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2. Aug 15, 2008

### Final

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 [Broken]

Last edited by a moderator: May 3, 2017