2 ships on a river...

[reverse]

This reminds me of the joke.

 

A kid walks to school behind the bus to save five dollars.

Later he got smarter and walked behind a private limo to save $200.

[Asimov Pupil]

lets say hypotheticaly you could break the chain with water current. It doesn't matter because the ship is not producing power so your ship would just drift. Hp still equals zero!

[Callipygous]

lets say hypotheticaly you could break the chain with water current. It doesn't matter because the ship is not producing power so your ship would just drift. Hp still equals zero!

 

 

anyone else think "hitpoints" when they see "hp"?

 

i wonder if they have 12 step programs for gamers...

[reverse]

I can see why Hp = 0 would upset you.

 

Isn’t the only question here.

 

Is horsepower a measure of Work?

 

And maybe,

 

can you do work without moving?

 

Security guards seem to get paid for it….???

 

http://www.learn.co.za/content/grade12/Science/phys_momentum/ForceWorkPower/Unit1/

[Spyman]

Is horsepower a measure of Work?

 

can you do work without moving?

 

Security guards seem to get paid for it….???

From Your own link:

Power: The rate of doing work = work/time

No Work without moving, only Force.

 

I also get paid without moving...

[Anindya]

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

If the boat drifts' date=' 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???[/quote']

Well I am not sure but in cars when the brakes are applied in full throttle there is a kind of reverse fprce generaed which is termed as brake horse power.

However I have this definition from the American Heritage Dictionary -

The actual or useful horsepower of an engine, usually determined from the force exerted on a friction brake or dynamometer connected to the drive shaft.

[Asimov Pupil]

I can see why Hp = 0 would upset you.

 

Isn’t the only question here.

 

Is horsepower a measure of Work?

 

And maybe' date='

 

can you do work without moving?

 

Security guards seem to get paid for it….???

 

[/quote']

 

no [math]W=Fd....................D![/math]

[RedAlert]

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

 

Wasn't that obvious....or am I misunderstanding the question (which I think I am).

[Asimov Pupil]

yeah

[J.C.MacSwell]

Relative to the water/current there is a transfer of power through the anchor, chain etc.

[RedAlert]

Well the anchor is meant to stop the ship from moving. How does it produce horsepower then? It produces none! Is it a motor powered anchor lol?

[reverse]

For every equation there is a person behind it.

 

What we are really talking about is nothing more that the correct way to apply the equation.

 

So why don’t we ask the troublemaker himself,

 

http://www.aerospaceweb.org/question/history/q0162b.shtml

[jcarlson]

but the force is not being exerted over a distance

 

It is being exerted over a distance relative to the water.

[reverse]

that's actually quite a good observation.

 

I like it.

 

So do you suppose Newton decided to take all his equations relative to the earth?

 

l

[Asimov Pupil]

but the anchor is attached to the ground so isn't the ship with respect to the ground?

[reverse]

Oi!,

 

(Slaps forehead with open palm)

 

Let’s get that original question over here and run an autopsy on it.

[doomtiki]

The first task which must be done is to integrate the power with respect to time so that the situation can be analysed at a single point in time. This means that work is dealt with instead of power. The current does work on the boat. The boat is not moved because the coefficent of friction (mu, dimensionless) times the weight (mass times gravitational acceleration) of the boat is greater than the amount of force the water exerts. The current does exert a force against the boat. The bottom of the river also exerts an equal force in the opposite dirrection through friction. Because both forces cancel the boat is not moved and no work is done becuase there is no change in linear displacement (dx). In the absence of friction, the boat would move down the river regardless of the anchor. In conclusion the anchor causes a force to be exerted in the opposite dirrection of the current, but does not do work or have power (dW/dt).

[jcarlson]

The first task which must be done is to integrate the power with respect to time so that the situation can be analysed at a single point in time. This means that work is dealt with instead of power. The current does work on the boat. The boat is not moved because the coefficent of friction (mu, dimensionless) times the weight (mass times gravitational acceleration) of the boat is greater than the amount of force the water exerts. The current does exert a force against the boat. The bottom of the river also exerts an equal force in the opposite dirrection through friction. Because both forces cancel the boat is not moved and no work is done becuase there is no change in linear displacement (dx). In the absence of friction, the boat would move down the river regardless of the anchor. In conclusion the anchor causes a force to be exerted in the opposite dirrection of the current, but does not do work or have power (dW/dt).

 

In the absence of friction, the boat would remain stationary while the river flowed around it because there would be no force applied to the boat by the water.

[doomtiki]

True, but either way the anchor is still not exerting any power due to the abscence of work.

[SketchTurner]

Ok what I believe is happening is the water acts upon the boat which pulls the anchor. The anchor pulls the Earth. Now due to the huge difference in mass noone would notice the effect of the Earth being pulled but effectively the kinetic energy lost by the water would be gained by the Earth

[Callipygous]

i dont think it works like that... "the earth" is kindof a closed system, which includes the water.

[SketchTurner]

Exactly. It incudes the water so the water has an effect on it. It's simple physics

[robotochan]

Asimov and others have been saying that no work is being done because no distance is moved, but is that no the same for the stationary boat using 1000hp to maintain equilibrium. So clearly you have to take your distance with relation to the water not the actual position in space. Meaning as the anchor is providing a force and is going a distance (relative to the water as previously explained) it is doing work. as the speed of the river in both cases is the same, i would say it would be doing 1000hp of work, but i cannot work out where this energy is comign from, in the engine example it is comign from the fuel, here i dont get it, is it e.p.e or strain energy or somthign, but that doesn't make sence as thats liek a gain of energy with regards to the system which is impossible. It is a rather confusing senario, but i dont think you can say as it isn't moving no work is bing done, as this would be the same for the motorised boat but we have been told it is doing work.

[DQW]

In the rest frame of the ships, no work is done in both cases.

 

In the rest frame of the water, the power consumed is 1000 HP in both cases.

[eon_rider]

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 ?

 

 

EDIT:

The anchor produces 500 horsepower as IT IS ANCHORED TO THE FIRST SHIP!

(not anchored to the shore)

 

The two ships are like one. The weight is doubled. So the anchor produces 500 horse power for the second ship.

 

Actually horsepower has multiple definitions depending on how it's applied so even if the second ship as I'm suggesting is anchored to the first ship I'm not sure if weight is even a variable affecting the distribution of horse power in this particular system.

 

 

LOL...

 

or there are multiple answers to the question depending on approach and/or other unknowns not revealed in the question. So several answers posted may already be correct. Not sure.