A shell is tied to the side of the boat.
The shell hangs 3 meters above water level.
The water rises 2cm an hour.
How much time will it take before water touches the shell?
Answer : The shell will never touch the water because it "goes with the flow" i.e. shell rises and falls with the boat.
Saiprasanna It is not mentioned that it is hanging to the boat anywhere in the question, may be you need to update it.