SUSPENSION BRIDGE PROBLEM

Question of the suspension bridge

The cable of a uniformly loaded suspension bridge hangs in the form of a parabola. The roadway which is horizontal and 100 m long is supported by vertical wires attached to the cable, the longest wire being 30 m and the shortest being 6 m. Find the length of a supporting wire attached to the roadway 18 m from the middle.

Think of the problem as a real problem that you have to calculate the length of the wire. It is a very interesting problem that helps one to understand where mathematics is used in real life situation.




  • It would be easy to visualize the problem if we have a diagram. So, let us draw a diagram.





SUSPENSION BRIDGE PROBLEM




  • Now let us plot a coordinate graph for this diagram












If we now solve using the coordinates of the parabola would get the answer. 

Let us take the point ( 50, 24 ) and solving we get 

Again using the point ( 18, y ) and solving we get 

This is the length between the point ( 18, y ) and the x-axis.
Therefore we have to add the length of the wire below the axis to this length so that we could calculate the length of the whole wire. 

Hence, the length of the wire is 3.11 + 6 = 9.11 m ( approximate ).

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