Question

A boat takes 2hrs to go 8km and come back in still water lake . The time taken for gng 8km upstream and coming back with water velocity of 4km/h is :

Chpt . Kinematics ( relative motion in 1d )
Class IX Medical

Answer 1

Time=distance/velocityVbr= 8km/hVrg=4km/hLet t1 and t2 be the time taken by boat to travel in upstream and downstream respectivelyUpstream=8-4=4Downstream=8+4=12T1=8/4=2hrT2=8/12=2/3Total time=2+2/3=2 hr and 40 mins or 160 mins