A body can remain at its current position only if all the external forces acting on it sum up to zero. For a body to be in **translational equilibrium**, it is necessary that

Example

When a 20 N weight is hung on a clothes line, the line sags as shown in diagram. Determine the tension in the clothes line.

Solution

Method 1

Consider the equilibrium of the section of the rope where the mass is hung.

Horizontally, S*F*_{x }= 0:

Vertically, S*F*_{y }= 0:

Substitute back into earlier equation:

Method 2

Because the three forces should add up to zero, they should form a closed vector triangle.

Using sine rule:

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**Demonstration**

50 g lifts 100 g

**Example Problems**

Picture Frame

Block on Slop

Buoy in River

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