Momentum Q

If fan is placed just behind the sails then acc. t o3rd law boat wont move

but if u dont attach fan just behind the sails and ,keep the fan to the side of the boat.
then the fan will be positioned so that the wind from it would hit the side of the edge of the sail. Due to Bernoulli principle,a vacuum, will be created and a differential pressure will drive the boat forward.

thanks guys.. :)

guys how can u say tht fan is an internal force...its not creating any air but instead it is circulating external air which can indeed provide an external force