Fluid mechanics conceptual question

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Discussion Overview

The discussion revolves around a conceptual question in fluid mechanics involving a beaker of water, a suspended metal body, and the reading on a digital weighing machine. Participants explore the effects of buoyancy and tension on the weight measurement, considering various scenarios and interpretations.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant presents a scenario where a beaker with water and a suspended metal body is weighed, asking for the new reading on the scale.
  • Another participant requests the original poster to share their thought process to facilitate better assistance.
  • Confusion arises regarding whether the total reading should include the buoyant force acting on the suspended body or if it should be subtracted from the total weight.
  • A hint is provided to consider the beaker, water, and mass as a single system and to analyze the forces acting on it, including the tension in the string.
  • Further clarification is sought about the tension in the string and its implications for the reading on the weighing machine, emphasizing the equilibrium of forces in the system.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the impact of buoyancy and tension on the weighing machine's reading. There is no consensus on the correct interpretation or final answer to the problem.

Contextual Notes

Participants note that the problem is a well-known question from a competitive examination, which may influence the complexity and depth of the discussion.

Who May Find This Useful

This discussion may be useful for students preparing for competitive exams in physics, particularly those interested in fluid mechanics and the principles of buoyancy and equilibrium.

alphabeta1720
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a beaker containing water is placed on the platform of a digital weighing machine. it reads 1100 grams. a metal body of density 8g/cc and mass 200 g is suspended in water in the beaker(without touching the walls of the beaker). it is attached by a suitable string fixed to some support. Now what will be the reading on the weighing machine. from the following options which one is correct? give reasons
a. 1100 g
b. 1125 g
c. 1275 g
d. 1300 g
 
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hi alphabeta1720! :wink:

show us what you've tried, and what you think the reason is, and then we'll know how to help! :smile:
 
tiny-tim said:
hi alphabeta1720! :wink:
show us what you've tried, and what you think the reason is, and then we'll know how to help! :smile:

my only confusion is whether it will be a total reading of 1300 or upthrust will be subtracted.
 
hint: consider the beaker the water and the mass as a single body (mass M + m, say) …

what are the forces on it?

is there any tension in the string? :wink:
 
tiny-tim said:
hint: consider the beaker the water and the mass as a single body (mass M + m, say) …

what are the forces on it?

is there any tension in the string? :wink:

that is the confusion i have about the tension of the spring. nothing else is giving in the problem and this is famous problem of KVPY. it is a competitive examination which is very prestigious at high school level. so anyone tell me the answer and also explain me. I am alplebeta.
 
hi alphabeta! :smile:
alphabeta1720 said:
my only confusion is whether it will be a total reading of 1300 or upthrust will be subtracted.
aradhya said:
that is the confusion i have about the tension of the spring. nothing else is giving in the problem and this is famous problem of KVPY.

what i was getting at is that the only external forces on the beaker-water-mass system are the weight, the tension in the string, and the reaction from the platform …

since the system is in equilibrium, they must add to zero

since common-sense tells you that there must be some tension in the string (you are ok with that, aren't you?), that shows that the reaction from the platform (which is the same as the reading on the weighing scale) must be less than the weight, doesn't it?

that should help you to work out the solution to the problem (as you know, on this forum we're not allowed to give you the answer, we only help you to find it yourself!) :smile:
 

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