a fan on a floating barge blows air at high speed toward the right.

a)will the barge move? if so, what direction? explain.
B) a sail is now put up on the barge so that the fan blows air towards the sail. will the barge move. if so, what direction? explain.

1 answer

a) The barge will move in the opposite direction that is pushes the air. Think of Newton's Third law here. The force of the fan blades upon the air equals the force of the air on the fan.

b) In this case the barge may move, but very little. Assuming no natural wind, the force of the fanned air hitting the sail will be nearly equal and opposite to the force of the air on the fan blades. The sail takes away the momentum of the air directed at it by the fan.