This model represents a drawbridge, attached to a wall at the red end. The suspending cable is attached at the 75% position and makes a 45-degree angle with the bridge deck. The bridge is of uniform construction so that the center of gravity is at the center of the span. Suppose we now wish to analyze the situation described in the text.

It should be obvious that the tension in the cable increases with increasing distance of the load from the castle wall. Click on the label for the 10-ton weight vector and set the location of that force to 100 percent of the bridge length. Then click the Action button to recalculate the other vectors. The maximum tension can be read from the vector label. If there is any doubt that this results in the maximum tension, try several other locations for the 10 ton weight.

To answer the second part requires us to recognize that removing the vertical load at the castle end of the bridge will facilitate the bolt replacement. Let's just delete the vertical reaction force vector and make the location of the 10-ton load movable. Then when the algorithm solves for equilibrium it will place the load vector at the appropriate place to relieve the stress on the bolts. Click on the vertical reaction force vector and click the delete button. Next click on the load vector and change its location from "fixed" to "movable". Then OK the vector editor. Click the Action button for the solution.

For details on the operation of the controls, see the Model Controls help page.