Car A and Car are at right angles to each other. Distance covered by Car A in 20sec(AB)= Speed × time =54×
5
18
×20=300m Distance covered by Car B in 20sec (BC)=72×
5
18
×20=400m In ΔABC AC2=BC2+AB2 [by Pythagoras theorem] ⇒ AC2=(400)2+(300)2 ⇒ AC2=160000+90000 ⇒ AC2=250000 ∴ AC=500m Hence, distance between Car A and Car B=500m.