It's a Drag

[tvp45]

In practice, a rudder. It's not important to the question though, since you know what the velocity is anyway. You could break it down into it's component forces like swansont says and work out just how drag would be required though, if that's your thing.

 

I disagree. It is important to the question if you use cos (theta). Calculation turns a very simple question into a complicated one that you just need to think about for a minute.

[swansont]

I disagree. It is important to the question if you use cos (theta). Calculation turns a very simple question into a complicated one that you just need to think about for a minute.

 

I think the point of the question is to look at the force in the direction of motion. I'm not sure if you'd consider the force on the rudder to be drag, if one were to assume that was restricting the lateral motion, since drag is a speed-dependent quantity and the speed in that direction is zero.

 

This is a physics 101 problem; one should try not to read too much into it.

[tvp45]

I think the point of the question is to look at the force in the direction of motion. I'm not sure if you'd consider the force on the rudder to be drag, if one were to assume that was restricting the lateral motion, since drag is a speed-dependent quantity and the speed in that direction is zero.

 

This is a physics 101 problem; one should try not to read too much into it.

 

No, I agree. I'm trying to not read anything at all into it. We have no way of knowing whether it's a rudder (which is not parallel to the direction of motion), zebra mussels on one side, or a sea anchor that keeps the barge in the middle. And, of course, you are completely right - if the horse slows down to munch some clover, you'll need some fenders on that side.

 

My question was meant to be of a Socratic nature: if the horse pulls on the barge with 400 lb, what prevents the barge from accelerating toward the horse?

[MrMongoose]

Maybe the boat slows down to munch some clover?

[alan2here]

Horse is more complex that most forces as Horse creates force up to the speed it is moving then doesn't supply any more. You will accelerate quickly up to horse speed then abruptly stop accelerating and stay at that speed.

 

Unlike a sail that will create constant force that gradually decreases with speed as you approach wind-speed and the drag force becomes equal to the sail force.

[Skye]

I'm not sure if you'd consider the force on the rudder to be drag, if one were to assume that was restricting the lateral motion, since drag is a speed-dependent quantity and the speed in that direction is zero.

 

This is a physics 101 problem; one should try not to read too much into it.

Err yeah, thinking about what actually stops the boat running aground is a force created by the boat travelling at an angle of attack, which is maintained by the rudder. Same way that lift is generated by a aeroplane. But probably not that relevent to the question.

[J.C.MacSwell]

I think the point of the question is to look at the force in the direction of motion. I'm not sure if you'd consider the force on the rudder to be drag, if one were to assume that was restricting the lateral motion, since drag is a speed-dependent quantity and the speed in that direction is zero.

 

This is a physics 101 problem; one should try not to read too much into it.

 

By convention there would be lift forces perpendicular to the flow and drag forces in the direction of the flow.