2 ships on a river...

[Externet]

Two identical ships next to each other in the middle of a river heading against the current; one at full throttle developing 1000 horsepower just counteracts the current and does not advance at all.

The other is anchored.

How many horsepower does the anchor produce ?

[Asimov Pupil]

none

[Callipygous]

?? i dont really know how to answer that since i dont know the exact definition of horsepower. the anchor is exerting force on the ground, does that count as producing horsepower?

 

asimovs answer sounds kinda right.

[Asimov Pupil]

[math]W=Fd[/math]

 

[math]P=\frac{W}{t}[/math]

 

[math]1hp=743w[/math]

 

there is no distance for the second ship

the first ships hp was measured from engine work

[Callipygous]

there is distance relative to the water, does that not count just because its touching land?

[Asimov Pupil]

oo i never though of that anyone got an answer

[Asimov Pupil]

what are we anchoring it to?

[Bettina]

If this is a trick question, the engine is developing 1000 horsepower to stay neutral in the current. The anchor is fixed to the ground and developing nothing. If some instrument were to measure the force being exerted on the anchor, I could maybe say it would be 1000 hp.....I think.

 

Bettina

[Asimov Pupil]

but the force is not being exerted over a distance

[Bettina]

I looked again and thought this.....

 

The ship is developing 1000 hp to maintain 0 forward motion. It drops the anchor to the bottom. The anchor has 0 force on it. Now the captain shuts off the engine and the ship begins tugging on the anchor with a force equal to 1000hp?........I think? Grrrrrrrr.

 

Bettina

[Callipygous]

it is being exerted over a distance if you measure according to the water instead of the land. the river is pushing on the boat, energy is going through the anchor and pushing on the ground to keep it from moving, essentially by pulling it forward through the water.

 

i dont know which is right, im just presenting this side of the arguement as best i can

[Bettina]

it is being exerted over a distance if you measure according to the water instead of the land. the river is pushing on the boat' date=' energy is going through the anchor and pushing on the ground to keep it from moving, essentially by pulling it forward through the water.

 

i dont know which is right, im just presenting this side of the arguement as best i can [/quote']

 

I would have thought that distance is irrelevent. It is the amount of work that the engine must produce to counteract the force of the current.

I too.....best I can.

 

Bettina

[coquina]

Two identical ships next to each other in the middle of a river heading against the current; one at full throttle developing 1000 horsepower just counteracts the current and does not advance at all.

The other is anchored.

How many horsepower does the anchor produce ?

 

OK - let's say that the current is running 6 knots (nautical miles per hour).

If the boat drifts, it will go down the river at 6 knots, so, in order to keep stationery, the engine has to produce adequate horsepower to generate a speed of 6 knots over the ground. (One speaks of two kinds of velocity with regard to marine navigation, speed over ground and speed through the water.)

 

The anchor doesn't produce horsepower. I am a moron when it comes to physics, but I would say that in basic terms, the anchor increases the friction to produce drag.

 

If you compared it to an automobile, you would say how many horsepower are generated by applying the brakes. None, right???

[Bettina]

I'm assuming we are allowed to measure the force on the anchor. I don't know what the rules are though.

 

Bettina

[Asimov Pupil]

we can measure the force on the anchor but the distance is what matters. Do we measure from the water or the ground the anchor is atached to?

 

i say its measured from the ground.

[Asimov Pupil]

and if it is then there is no work done therfore no power and no Horse power

[reverse]

I reckon that no work is done, as no energy is required to keep the system in equilibrium.

 

The river could stop and the ship would stay in position.

 

This is one of those point of view tricks I think.

 

found this link to back up my position.

 

http://id.mind.net/~zona/mstm/physics/mechanics/energy/work/work.html

and this

http://www.daviddarling.info/encyclopedia/H/AE_horsepower.html

[Asimov Pupil]

and another thought is if you calculate the force on the anchor by the water it is not generated by the water therefore you have no force by the ship.

 

therefore you have no force or distance

[reverse]

But what if you increase the speed of the water until it breaks the chain???

 

That seems to indicate that all those atoms of iron were doing something to keep in equilibrium.

[Newtonian]

The speed of water current is never going to be sufficient to break the chain.I could comfortably stand on the river bank holding onto the ship with a length of rope

[Spyman]

I could comfortably stand on the river bank holding onto the ship with a length of rope

I would really like to look when You try this...

 

I have actually done some small boat trips in fast floating rivers and I know from experience it's very tough just holding on to a small boat from the bank.

 

In this case it would be exactly like holding on to a ship "at full throttle developing 1000 horsepower" on a lake, that is at standstill.

 

Do You know how to waterski ?

[reverse]

Ok, say we make them two torpedoes, both submerged, one chained - the other not.

This way we can ignore the boats planing effect,

and the form drag may now become significant.

[Spyman]

Ok, say we make them two torpedoes, both submerged,

Then You would need a divingsuit...

 

"1000 horsepower" is still "1000 horsepower" it makes no difference, the friction from the propeller is under water in both cases.

 

Why don't You say they are two racing cars instead and move the power from the engine via friction from the propeller to the tires.

(Both are being pushed back by elephants, one holds the position with engine power and friction from the tires and the other holds the position by the ancor.)

 

Let's say You are attached to a rope behind the car, suddenly the elephants jumps away...

 

Do You still think You are "superman" and can hold the car ?

 

EDIT: Sorry reverse when reading through this thread again I realize I mixed You up with Newtonian.

 

- I apologize !

 

The flow of the river could break the chain if it increased, without the need to go submerged.

(Thats the reason for using a chain instead of rope on large ships.)

[coquina]

The speed of water current is never going to be sufficient to break the chain.I could comfortably stand on the river bank holding onto the ship with a length of rope

 

The current in the C&D canal can run as fast as 6 knots. It is not unusual to have a current in the Chesapeake Bay of 2kts. You have to think about the surface area of the bottom of the boat that is being acted on by it. Even a smaller pleasure boat, about 40' long with a 15' beam has almost 600 sq ft of surface area.

 

We haven't defined the size of the "ships" but here is a link that gives various ship sizes: http://www.rpsoft2000.com/shipsize.htm It would not be at all unreasonable to use 1000 x 100, so that is approximately 100,000 feet of bottom. (I didn't allow for the ship narrowing at the bow, which would decrease surface area, neither did I allow for the fact that part of the bottom is on an angle, which would increase it.)

 

In any case, the original question was "how much horsepower does the anchor produce" - none.

 

The current can generate horsepower. Around here, there used to be "tidemills" that used the velocity of the current to turn a water wheel.

[Spyman]

In any case, the original question was "how much horsepower does the anchor produce" - none.

That is correct, Force and Power is not the same thing !

 

Force, in this case, is how hard the water pushes on the ship, which is countered by the force of the anchor.

 

Horsepower is how FAST a Force is able to accelerate a body, which for the anchor is Zero.

(The anchor is not moving either the water or the ship.)

 

The engine on the other ship is moving a lot of water very fast to counteract the flow of the river.