How Does Moving a Boat Affect Scale Readings and Torque?

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Homework Help Overview

The discussion revolves around a physics problem involving torque and scale readings related to a boat on a trailer. The original poster presents a scenario where the scale reading changes as the boat is moved, prompting questions about the setup of equations and the nature of forces involved.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the setup of torque equations and question the signs of the moments involved. There is a focus on understanding why the scale reading does not directly contribute to the torque calculations.

Discussion Status

Some participants have provided feedback on the setup of the equations, indicating that the original poster's approach appears sound. The discussion is ongoing, with participants clarifying concepts related to torque and forces acting on the trailer.

Contextual Notes

Participants are examining the implications of the scale readings and the forces acting on the trailer, questioning the assumptions made in the torque calculations. There is a focus on understanding the relationship between the scale reading and the forces at play.

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Homework Statement



A trailer carrying a boat is supported by a scale which initially reads 48kg. The boat is moved 0.15m further back on the trailer. The scale now reads 37kg. What is the mass of the boat?

boat.png






Homework Equations



torque = F(perpendicular) * d
For equilibrium:
Sum moments = 0
Sum Fy=0
Sum Fx=0


The Attempt at a Solution



Taking moments about the wheel:

(48*9.81*6)+9.81*m*x=0
(37*9.81*6)+(9.81*m*(x-0.15))=0

Two equations and two unknowns (m and x). Solve.


 
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canicon25 said:

Homework Statement



A trailer carrying a boat is supported by a scale which initially reads 48kg. The boat is moved 0.15m further back on the trailer. The scale now reads 37kg. What is the mass of the boat?

boat.png

Homework Equations



torque = F(perpendicular) * d
For equilibrium:
Sum moments = 0
Sum Fy=0
Sum Fx=0

The Attempt at a Solution



Taking moments about the wheel:

(48*9.81*6)+9.81*m*x=0
(37*9.81*6)+(9.81*m*(x-0.15))=0

Two equations and two unknowns (m and x). Solve.
In both cases, the two moments should have the opposite signs since one force wants to cause the trailer to rotate clockwise, and the other, counter-clockwise.

Other than that, your set-up looks fine. What's your question?
 
my original question was simple am i going about setting up the equation correctly.

but my question now is why are the two moments opposite in sign.

if there is a measure of 46kg on the scale why is it not a component of the force acting down on the scale?
 
Because you're calculating the moment acting on the trailer. The trailer pushes down on the scale, but that force doesn't exert a torque on the trailer. It's the reaction force, the scale pushing up on the trailer, that is responsible for the torque on the trailer.
 
Last edited:

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