Discover the Boat's Speed: Solving for dc/dt on a Pier with 6m of Rope Out

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Homework Help Overview

The problem involves a scenario where a man is pulling in a rope attached to a boat, and the goal is to determine the speed at which the boat approaches the pier. The context includes elements of related rates in calculus, specifically focusing on the relationship between the lengths of the sides of a right triangle formed by the rope, the height of the man's hands, and the distance of the boat from the pier.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the setup of the triangle and the definitions of the sides, questioning which side represents the hypotenuse and how the rates of change relate to the lengths involved. There is also a focus on the signs of the rates, particularly regarding the direction of the rope being pulled in.

Discussion Status

The discussion is active, with participants exploring different interpretations of the geometric setup and the implications of the rates of change. Some guidance has been offered regarding the correct identification of the hypotenuse and the signs of the rates, but there is no explicit consensus on the final interpretation.

Contextual Notes

Participants are working under the assumption that the height of the man's hands is fixed, and there is a specific focus on the rate at which the rope is being pulled in, which is noted to be 0.4 meters per second.

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A man on a pier pulls in a rope attached to a small boat at the rate of 0.4 metres
per second. If his hands are 3 metres above the place where the rope is attached,
how fast is the boat approaching the pier when there is 6 metres of rope out?


Is the question asking for dc/dt ? c is the hypotenuse.
 
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Think again about how you are setting up the triangle. Look at it from a 'side-on' view i.e. you are seeing the side of the man's face, as opposed to viewing it from the front.

Which piece represents the hypotenuse? Is it the height of the man's hand from the water, the rope, or the water? What do the other two sides of the triangle represent?
 
Yeah? Well the height "y" is fixed is equivalent to 3, and dx/dt is unknown, dc/dt= 0.4, right?
 
No, dc/dt = -0.4. The rope is being pulled in (getting shorter), not being let out.
 

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