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.
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.

We realize that the vertex is at the absolute bottom of the link. The beginning of the facilitate plane is taken as the vertex of the parabola, while its upward hub is brought the positive

    \[y\text{ }\text{ }axis.\]

Diagrammatic portrayal is as per the following:

NCERT Solutions for Class 11 Maths Chapter 11 – Conic Sections image - 3

Here,

    \[AB\text{ }and\text{ }OC\]

are the longest and the most brief wires, separately, appended to the link.

DF is the supporting wire appended to the streets,

    \[18m\]

from the center.

Along these lines,

    \[AB\text{ }=\text{ }30m,\text{ }OC\text{ }=\text{ }6m,\text{ }and\text{ }BC\text{ }=\text{ }50m.\]

The condition of the parabola is of the from

    \[{{x}^{2}}~=\text{ }4ay\]

(as it is opening upwards).

The directions of point A are

    \[\left( 50,\text{ }30\text{ }-\text{ }6 \right)\text{ }=\text{ }\left( 50,\text{ }24 \right)\]

Since,

    \[A\left( 50,\text{ }24 \right)\]

is a point on the parabola.

    \[\begin{array}{*{35}{l}} {{y}^{2}}~=\text{ }4ax  \\ {{\left( 50 \right)}^{2}}~=\text{ }4a\left( 24 \right)  \\ a\text{ }=\text{ }\left( 50\times 50 \right)/\left( 4\times 24 \right)  \\ =\text{ }625/24  \\ \end{array}\]

Condition of the parabola,

    \[{{x}^{2}}~=\text{ }4ay\text{ }=\text{ }4\times \left( 625/24 \right)y\text{ }or\text{ }6{{x}^{2}}~=\text{ }625y\]

The

    \[x\text{ }\text{ coordinate}\]

of point

    \[D\text{ }is\text{ }18.\]

Henceforth, at

    \[x\text{ }=\text{ }18,\]

    \[\begin{array}{*{35}{l}} 6{{\left( 18 \right)}^{2}}~=\text{ }625y  \\ y\text{ }=\text{ }\left( 6\times 18\times 18 \right)/625  \\ =\text{ }3.11\left( approx. \right)  \\ Thus,\text{ }DE\text{ }=\text{ }3.11\text{ }m  \\ DF\text{ }=\text{ }DE\text{ }+EF\text{ }=\text{ }3.11m\text{ }+6m\text{ }=\text{ }9.11m  \\ \end{array}\]

Hence, the length of the supporting wire attached to the roadway 

    \[18m\]

from the middle is approximately

    \[9.11m.\]