Diameter of the circle = 40 cm

Radius (r) of the circle = 40/2 cm = 20cm

Let AB be a chord (length = 20 cm) of the circle.

In ΔOAB, OA = OB = Radius of circle = 20 cm

Also, AB = 20 cm

Thus, ΔOAB is an equilateral triangle.

θ = 60° = π/3 radian

We know that in a circle of radius r unit, if an arc of length l unit subtends

an angle θ

Thus, the length of the minor arc of the chord is 20π/3 cm