• May 11th 2013, 06:43 PM
dumbblonde
Two electic poles AB and DC are 50m high and 100m long apart. An electrical wire is suspended between B and C and it assumes the shape of a parabola under its own weight. The maximum sag at the middle is 10m.

How high is the wire above point X, given thar XD= 25m

How do you get this answer?
• May 11th 2013, 07:40 PM
MarkFL
I would orient my coordinate axes such that the vertex is at the origin. And so we know:

y(0)=0

y(±50)=10

A parabola opening upwards, with its vertex at the origin can be written:

y=ax^2 where 0<a

Now, using the point (50,10), can you determine the parameter a?

Once you do this, then evaluate y(25)+40 to find the height of the wire above the ground at X.

edit: Normally I like to use LaTeX, but it is not working at the moment.
• May 11th 2013, 09:34 PM
dumbblonde
i don't know how to determine the parameter of a :/
• May 11th 2013, 09:47 PM
MarkFL
In the equation $y = ax^2$, let x = 50 and y = 10, then solve for a.