Work done to bring the Earth to rest

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Homework Help Overview

The discussion revolves around the concept of work done to bring the Earth to rest, specifically examining the relationship between centripetal force and work in the context of circular motion. Participants explore the implications of applying forces to halt the Earth's motion and the theoretical underpinnings of such a scenario.

Discussion Character

  • Conceptual clarification, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the idea of using centripetal force as a starting point for solving the problem, questioning the validity of this approach. There are attempts to reconcile the concept of anticentripetal force with the work-energy theorem and the nature of forces acting on the Earth.

Discussion Status

The discussion is active, with participants offering insights into the misconceptions surrounding centripetal force and work. Some have recognized errors in their reasoning, while others are questioning the feasibility of the scenario presented. The exploration of different interpretations and approaches is ongoing.

Contextual Notes

There is a mention of limitations regarding the practicality of bringing the Earth to rest, suggesting that the discussion may involve hypothetical scenarios rather than realistic applications. Participants also reference the need for a mechanism to achieve such an outcome, indicating a lack of concrete solutions.

walking
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I know how to solve this using work energy theorem but how can one solve it starting from the fact that net force is centripetal? My attempt was "this means we only need an "anticentripetal" force of same magnitude, but centripetal force does 0 work hence new force also 0 work to counter it". This is wrong but I don't see why.
 
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The word centripetal is not a force but a direction. The force in this case is gravity.
 
An anticentripetal force applied to Earth would indeed do no work (at first), but it would also merely cause Earth to cease its acceleration, so its path becomes straight instead of curved. It wouldn't in any way bring Earth to rest as the problem statement asks.
 
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walking said:
starting from the fact that net force is centripetal
I don't understand. Who is saying you could start from that fact to answer the question?
A block sliding horizontally on a frictionless surface has no net force on it. How can you use that fact to find the work needed to halt it?
 
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walking said:
View attachment 279537

I know how to solve this using work energy theorem but how can one solve it starting from the fact that net force is centripetal? My attempt was "this means we only need an "anticentripetal" force of same magnitude, but centripetal force does 0 work hence new force also 0 work to counter it". This is wrong but I don't see why.
As you have limited internet time, I would recommend to consider the trajectory of the planet like it was linear and its movement as of constant velocity.
That would not be different than a problem of calculating the work required to stop a car from certain speed.
 
Thanks everyone, I understand where I went wrong now - I was trying to stop an object moving in circular motion by stopping its circular motion, but this doesn't stop the object (by NI)!
 
It's all very well calculating a number like this, but how would it be possible to bring the Earth to rest? Unless we have some sort of mechanism in mind, it seems like a pointless calculation.
 

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