Question

A chord AB of length 10cm is drawn inside a circle of radius 5 cm. Write the measures of the arcs formed

Answer 1

The answer is obviously π,π, so the arc length is πr which is 5π cm
So your chord will neatly split the circle in half, giving two congruent 180∘arcs each of length 5π cms.

Answer 2

they gave that length of the chord AB is 10 and the radius is 5 
so that means the chord is the diameter of the circle 

so by taking a semi circle we it is $\frac{2 \pi r }{2}$

which means the legth of the arc is 5$\pi$