General Knowledge - Physics - Discussion

Dear all,

The boat will not move. Suppose the fan pushes an air molecule and in turn get pushed in opposite direction. Now, this molecule hits the sail of the boat and imparts the same momentum to the sail and hence boat.

In total two forces act on boat forward and backwards----hence zero motion.

This is similar to a person sitting on a boat and pushing it from inside--the boat won't move-----man pushes the boat in +x direction and boat pushes the man in -x direction as the man is on boat it means the boat is being pushed in -x direction----hence boat is pushed in +x and -x direction. No resultant motion.

This is in tune with newton second law --which states that only external force can change the momentum of a body and not internal forces. F (ext) =dP/dt.

The boat won't move unless it is equipped with provisions to transfer the thrust generated on fan to the body of the boat.

It is applicable for all scales of fans. So in the question, it is not clearly mentioned.

Even though there is an application of Newton's third law. As the action force by the fan receives reaction to itself. Not to the boat on this case. This is the reason why ships and watercraft are equipped with an arrangement called thrust block.

The boat will move. The air which is propelled by the fan will give an equal and opposite reaction/force to the fan and the fan will tend to move and as the fan is attached to the boat the boat will tend to move. If this force is more than the threshold force to move the boat the boat will definitely move in a direction opposite to the motion of the air. This simple principle is used in aeroplanes where the air is heated to get more thrust.

As the fan is attached to a simple boat it will move in opp. Direction due to newton's 3rd law.

But given boat is a sailboat.

As fan exert a force on the sail (the huge cloth attached to the boat to enable the boat move with wind energy) boat will not move because sail and fan are attached to the same boat.

It like a man sit in a trolly exert a force on the trolly. As a result net force is zero and trolly remains stationary.

Actually may be a little bit movement will be there but firstly when fan produces air then the sail gets affected which makes the boat to move in opposite direction to the movement through force of air to the boat. And that leads to null and makes boat to be at initial point only as it is. i.e. Stationary. So B is somehow correct.

I think the boat moves in the same direction in which the air blows. This is due to the sail pulling the boat in the same direction as the air. Had it been a fan (assumed to have a high thrust capability) fitted on a boat without a sail, the boat would've moved in the opposite direction just like a jet engine moves an aircraft.

Question is totally unclear to describe. The required information is whether the fan is mounted where. Whether it will produce thrust to move a boat. If it is mounted on the boat which can not create any impact on stability of the boat then boat will at least have movement up and down which is not an option given here.

The boat will move because of the reaction provided by the air (in the opposite direction).

This is the similar case as the jet engine, air is of certain momentum is sucked and by combustion of fuel its momentum increases so the net force on the jet will be equals to the rate of change of momentum.

The boat will move people. As there is no given information about the weight of boat or the thrust provided by fan, so we have to assume both the quantities and according to that the boat will move.

And the fan is also attached to the boat for the people who didn't even read the question carefully.

It would depend that the boat will move or not. It will not move when the fan is placed in the perpendicular direction. Similarly, it will move when the fan is placed in the horizontal direction as in the case of a hovercraft. I think that in this case, it is telling of the first case.