Solving Boat Speed & Distance with Drag Force

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Homework Help Overview

The discussion revolves around a physics problem involving the motion of a boat on a lake, where the boat experiences a drag force that is dependent on its instantaneous velocity. The participants are tasked with finding an expression for the speed of the boat over time, as well as the time and distance it takes for the boat to come to a stop.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the implications of the drag force being a function of the boat's instantaneous velocity, leading to confusion about the correct approach to derive the speed function v(t). There are attempts to express v(t) and find time and distance when the speed reaches zero, but uncertainty about the parameters α and β complicates the process. Some participants suggest rearranging the equations to separate variables for integration.

Discussion Status

The discussion is ongoing, with participants sharing their attempts and expressing confusion about the results. There is acknowledgment of mistakes in the formulation of the drag force, prompting a reevaluation of previous calculations. Guidance has been offered regarding the integration process and the need to clarify the definitions of the parameters involved.

Contextual Notes

Participants note the lack of specification for the parameters α and β, which adds to the complexity of the problem. There is also mention of challenges in communicating mathematical expressions effectively, particularly when using images instead of typed equations.

Macykc2
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Homework Statement


A boat with initial speed vo is launched on a lake. The Boat is slowed by the water by a force F=-αeβv. Find an expression for the speed v(t), and find the time and distance for the boat to stop.

Homework Equations


Drag force F=-αeβv
alpha and beta are not specified as to what they represent.

The Attempt at a Solution


I have an attached attempted solution, I'm just kind of confused on my results, I feel like it makes sense but at the same time it doesn't. My confusion lies in that I try to imagine using my derived v(t) equation but the drag force is constantly changed based on the instantaneous velocity at any moment, the v in the force equation is what throws me off, and makes me think I need to use a different approach.
Once I found my v(t) I found time when v(t)=0, then I found velocity as a function of position to find distance when v=0.
But again, now that I look at it, the v that is apart of e should probably be 0 as well, then the positions and times won't be affected by the drag force...
 

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Macykc2 said:

Homework Statement


A boat with initial speed vo is launched on a lake. The Boat is slowed by the water by a force F=-αeβv. Find an expression for the speed v(t), and find the time and distance for the boat to stop.

Homework Equations


Drag force F=-αeβv
alpha and beta are not specified as to what they represent.

The Attempt at a Solution


I have an attached attempted solution, I'm just kind of confused on my results, I feel like it makes sense but at the same time it doesn't. My confusion lies in that I try to imagine using my derived v(t) equation but the drag force is constantly changed based on the instantaneous velocity at any moment, the v in the force equation is what throws me off, and makes me think I need to use a different approach.
Once I found my v(t) I found time when v(t)=0, then I found velocity as a function of position to find distance when v=0.
But again, now that I look at it, the v that is apart of e should probably be 0 as well, then the positions and times won't be affected by the drag force...
Posting working as an image makes it hard to comment on individual lines. (It can also be hard to read, but yours is ok.)
Better to take the trouble to type the equations in, but if you must post images please number all the equations.

You cannot integrate a function of v just by multiplying it by t. v is a variable.
Rearrange the equation so that all the references to v are on one side and t on the other (including dv, dt).
 
I figured that's what i had to do, I took a look at it after I posted and tried some other things including that, and although I do get results it's once again hard to see if it makes sense, as they do not specify what alpha and beta are.

Also I will try in the future to just use this site instead of a picture, I'm just not good with that math function as I've never used it.

I ended up with v(t)=##\frac{1}{β}##ln(eβvo - ##\frac{αβt}{m})## but as I said, it's hard to know if what I did is right with the lack of info.
 
I also just noticed a very crucial mistake, this whole time I've been writing eβv as e-βv, so I need to re-do everything...
 

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