Find the length of a rope by which a cow must be tethered in order that it may be able to graze an area of 9856 sq meters.

clearly the cow will graze a circular field of area 9856 sq m and radius equal to the length of the rope.

Let the length of the rope be r mts 

then,  $\mathrm{\pi r}2=9856 \Rightarrow r2=\frac{9856\times 7}{22}=3136 \Rightarrow r =56m$