General Knowledge - Physics - Discussion

Discussion :: Physics - Section 1 (Q.No.57)


On a stationary sail boat, air is blown from a fan attached to the boat. The boat

[A]. moves in opposite direction in which the air is blown
[B]. does not move
[C]. moves in the same direction in which air blows
[D]. spins around

Answer: Option B


No answer description available for this question.

Srijoni said: (Nov 2, 2011)  
Why the boat does not move?

Ajay said: (Feb 2, 2012)  
Becouse every action there is equal and opposit reaction. So for movement of a body there is need of reaction, which is not available to boat becouse fan is monted on boat itself.

Shiyas said: (Feb 15, 2012)  
This case is similar to propeller aircraft in which the propeller is mounted on the aircraft.when propeller turns air is blown and as the momentum of air changes it imparts reaction on the blades of the propeller,which in turn moves the air craft.

Shiyas said: (Feb 15, 2012)  
The boat will move!!!If sufficient thrust is produced.

Amit said: (Feb 21, 2012)  
I agree with Shiyas, It will definitely move if force is enough.

Banshi Dhar said: (Apr 16, 2012)  
I totally disagree with amit and shiyas because the force [thrust] acts on a body[boat] in a perpendicular direction.

Jyoti said: (May 31, 2012)  
Please suggest a particular reason for no motion.

Anoop C Raj said: (Jun 22, 2012)  
Air is less denser than water. So large fan is needed. Otherwise it must be a hovercraft.

Ramanuj said: (Nov 30, 2012)  
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.

Sudha said: (Mar 15, 2013)  
Theoritycally the boat should move(whatever be the thrust).

Archit Singhal said: (Jun 11, 2013)  
I can't understand the reason of no moving. Because hovercraft is a device which has a fan mounted on it and it can move in every surface. So why is it not?

Aravind said: (Jul 19, 2013)  
When the fan pushes the sail by blowing air, the air also pushes the fan in opposite direction. As the fan is a part of the boat, the vector sum of the momenta of the fan and the boat is zero. The boat will only move if some external agency applies force on it.

Prakash said: (Jul 20, 2013)  
All dear buddies the boat does not move because the air is blown from the Fan not to the Fan So it doesn't receive any thrust or force hence it does not move.

Alia said: (Aug 24, 2013)  
Answer is B because by newton's third law of motion every action has opposite & equal reaction but here the boat will not move because the force is not sufficient to make the boat to move & for newton's third law mass must be equal to form equal reaction.

Kartikeya said: (Oct 23, 2013)  
If the boat does not moves then I can also give a reason that car will not move because engine is mounted to it.

The fan is capable of producing enough thrust to move the boat.

I disagree with @Banshi dhar and @Ajay.

Sid said: (Nov 27, 2013)  
The weight of the boat is not mentioned. In a water surface the friction is approximately zero. So according to newton's 3rd law the boat must move.

Prasuna said: (Dec 5, 2013)  
If there is sufficient force definitely boat will move.

Aiswarya said: (Jan 6, 2014)  
Please tell me what is the reason for it.

Dhasaradan said: (May 6, 2014)  
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.

Priyansh said: (Jul 3, 2014)  
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.

Aswathiachu said: (Aug 3, 2014)  
It will definitely moves in opposite direction in which in which air is blown.

Kiran said: (Aug 17, 2014)  
See practically take a fan tag it on small boat definitely it moves.

Man said: (Nov 18, 2014)  
It depend upon the angle of fan.

Prasanth said: (Jan 30, 2015)  
A sailboat is a boat propelled partly or entirely by sails. The sail neutralizes the thrust produced by FAN so the boat won't move.

Paimon Dkhar said: (Mar 27, 2015)  
A stationary sail boat does not move because the boat is tight with a rope.

Ankur said: (Jun 3, 2015)  
If its so, on what principle do hovercraft run, I think its the fat that pushes the air back. Isn't it?

Rks said: (Jul 25, 2015)  
The correct question should be on a stationary sail boat, air is blown (at the sail) from a fan attached to the boat. The boat they miss the main detail.

Rahul said: (Aug 31, 2015)  
Why a helicopter will fly but boat will not?

In both case there is a fan making a force in opposite direction.

Shivam said: (Aug 31, 2015)  
May be because it doesn't create such impact to move boat. Air just work as regular fan.

Law Of Energy said: (Jan 29, 2016)  
Dear friends, if the fan is operated through electricity, then that extra electric energy must show some effect when it becomes mechanical! by law of conservation of energy.

Tarun said: (Mar 24, 2016)  
The boat can move in the opposite direction of the fan. As there is not a description of the size of the fan. That's why the answer is correct, otherwise, AIRBOATs are there.

Surender Singh said: (Apr 25, 2016)  
Boat will move in the opposite to the direction of air is blowing because the mass of air is being a drag by a fan and at air will give thrust to the boat.

Maryam said: (Jul 25, 2016)  
I can't understand why boat will not move, And the answer is totally wrong.

According to me, it should move.

Gaurav said: (Jul 27, 2016)  
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.

Ashita Verma said: (Aug 12, 2016)  
Why does the boat does not move?

Teena said: (Sep 10, 2016)  
It is mentioned that fan is attached to the boat. Not that it is on the boat.

The boat will definitely move in the opposite direction as per as Newton's THIRD law of motion.

Shreyas Shrihari Taklikar said: (Dec 2, 2016)  
Boat will not move because external force is nedded to move boat and fan is blowing air which is internal force. So their must be an external for producing movement of boat.

Yousuf Shah said: (Dec 11, 2016)  
It will move in opposite direction.

Khan said: (Dec 23, 2016)  
It has to move.

Aaryendra Chhabra said: (Jan 8, 2017)  
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.

Arsh Virk said: (Jan 9, 2017)  
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.

Rajesh said: (Jan 17, 2017)  
Fan attached with helicopter lifts the helicopter upward the same way boat will move.

Anonymous. said: (Feb 4, 2017)  
The boat should move in the flow of air.

Surinder Singh said: (Mar 27, 2017)  
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.

Ijom Ninu said: (May 28, 2017)  
Question is not clear.

Because whether the fan has been fitted inside compartment for air circulation or it has been fitted on the edge of boat? in two cases, it will have differnt answer, for first, it will nor move, for second, it will move.

Navin Sridhar said: (Jun 13, 2017)  
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.

Shravan said: (Jul 3, 2017)  
It moves in the same direction in which the air is blown.

Maahi said: (Jul 8, 2017)  
It will move in opposite direction. But the thrust produced by the fan should be greater than the weight of the boat.

Maahi said: (Jul 8, 2017)  
Question is not appropriate!

If the fan is attached to a boat and directed toward its flaps. Then it will not move.

Varun Dhawan said: (Sep 7, 2017)  
Answer is the boat will not move.

As the air is blown on fan so to move forward fan give equal and opposite reaction to boat Ian the opposite direction s boat will be at the same place.

Saurabh said: (Oct 26, 2017)  
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.

Chemiroc said: (Jan 11, 2018)  
Then what is the principle of airboat?

Upendra said: (Feb 24, 2018)  
As per Newtons third law boat will move in opposite direction.

Abhinand said: (May 31, 2018)  
B is correct. When the fan pushes the sail by the air then air also pushes the fan in the opposite direction. Since fan is also a part of the boat, the vector-sum of the momenta of fan and boat is zero.

Shubham Kumar said: (Jul 31, 2018)  
According to me it will move in opposite directions of blow of the blow of the air by fan because in reaction of the force by fan atmosphere will also exert force which will be equal to magnitude of the force of fan but opposite in direction of air blow by fan.

Elnathan said: (May 13, 2019)  
The boat will move according to Newton's third law.

Mani Kandan said: (Nov 5, 2020)  
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.

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