If the arc is a 1/4 circle why not draw it ?
This shows it slightly longer that the 5m ??
But if this a chord length as you just drew how is the to supported ?
With a semi-circle the diameter [d] needs to be just under 6.4m for a half-circumference of 10m long…
10 = Pi * d / 2
d = 2 * 10 / Pi = 6.37m