Question

a farmer moves along the boundry of a square field of side 10 m in 40 sec. what will be the magnitude of displacement of the farmer at the end of 2 minutes 20 sec from his initial position?

Answer 1

so his speed=distance/time=10/40=0.75 m s-1
time taken t=2 min 20 sec=2*60+20=120+20=140 s
so distance covered is 140(0.75)=105 m
As it is square field 
the man completes 2 rounds and then covers 25 m more
so the final displacement is 11.180339887498948482045868343656 
 

Answer 2

SQ ABCD [fig.]
he starts from A and will reach the opp. corner i.e. C  in 140 sec.
 displacement = AC
                   AC²=AB²+BC² 
                          =10²+10²
                          =100+100
                 AC²=200
                AC=√200
                 AC =14.14m