An arch is in the form of a parabola with its axis vertical. The arch is 10 m high and 5 m wide at the base. How wide is it 2m from the vertex of the parabola?
Let AB be the parabolic arch having O at the vertex and the vertical line OY as the axis.
The parabola open upwards
∴ Its equation is of the form ...(i)
Width of the arch, LM = 5 m
OM = 2.5 m
Height of the arch, BM = 10 m
∴ Co-ordinates of point B are (2.5, 10)
Since point B lies on the parabola
∴
∴ From (i), the equation of the parabola is:
or ...(ii)
We have to find the width PQ of the arch at a distance ON = 2 m from the vertex.
Let PQ = d NQ =
∴ Co-ordinates of point Q are
Putting it in (ii), we get
Hence, the width of the arch = d = or 2.23 (approx).