Let us consider a boat which moves with a velcity `v_(be)=5 km h^(-1)` relative to water, At time `t=0`, the boat passes through a piece of cord floating in water while moving downstream. If itturns back at time `t=t_(1)`, when and wher does the boat meet the cork again ? Assume `t_(1)=30 min`,

Explanation

Consider an observer attached with cork. The boat has same speed upstream and downstream relative to cork. Hence., if the boat travels for 30min. while moving away from cork, it travel the same time while approching the cork.
Therefore the boat meet thecork at
T=2t = 60 min = 1h
The distance travelled by boat in this time,
`S=V_(BW) xx T = 5 xx 1= 5`km