Calculating Forces at A and B on Shelf in Slot

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Homework Help Overview

The discussion revolves around calculating the forces exerted on a wooden shelf by a support slot, specifically focusing on the forces at points A and B. The shelf has a mass of 7.7 kg and is subjected to torque due to its placement in a vertical support. Participants are attempting to determine the force at point A while considering the equilibrium of torques.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the requirement that the sum of torques must equal zero and express uncertainty about their calculations. Some question the impact of using different values for gravitational acceleration on their results.

Discussion Status

There is an ongoing dialogue where some participants have identified mistakes in their calculations after reviewing their work. Others express a lack of confidence in their answers, indicating that the discussion is productive but lacks a definitive consensus on the correct approach or solution.

Contextual Notes

Participants mention the importance of gravitational acceleration values in their calculations and the challenges of identifying mistakes without sharing detailed workings. There is a recognition of the potential for errors in the setup or assumptions made regarding the forces acting on the shelf.

elf197320501
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Homework Statement


When a wood shelf of mass 7.7 kg is fastened inside a slot in a vertical support as shown in (Figure 1) , the support exerts a torque on the shelf. Assume that the slot exerts two vertical forces on the shelf, at points A and B.
Giancoli7.ch9.p80_1.jpg

Determine the force exerted on the shelf by the support slot at A.

Homework Equations

The Attempt at a Solution


I know that the sum of the torques has to equal 0 and that the forces at A and CM is downwards, and upwards at B but I can't seem to get the correct answer (the correct answer is -566N)
 
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What did you get for an answer?

Edit: I didn't get that answer either. But I don't have a lot of confidence in my answer because I know from experience that I make lots of mistakes. :)
 
Last edited:
I got the "right" answer. Use g=9.8 not 9.81 or 10.
 
Thanks @CWatters. Because of your post, I want back and reviewed my work and found my mistake. My mistake was greater than what would be caused by using different gravity values. And yes, 9.8 gives the right answer.
 
elf197320501 said:

Homework Statement


When a wood shelf of mass 7.7 kg is fastened inside a slot in a vertical support as shown in (Figure 1) , the support exerts a torque on the shelf. Assume that the slot exerts two vertical forces on the shelf, at points A and B.
Giancoli7.ch9.p80_1.jpg

Determine the force exerted on the shelf by the support slot at A.

Homework Equations

The Attempt at a Solution


I know that the sum of the torques has to equal 0 and that the forces at A and CM is downwards, and upwards at B but I can't seem to get the correct answer (the correct answer is -566N)
Please post your working. A bit hard to find your mistake otherwise.
 

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