How much work is required to stop an electron

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Homework Help Overview

The discussion revolves around calculating the work required to stop an electron, specifically focusing on its kinetic energy and the implications of sign in the work calculation.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to calculate the work using the kinetic energy formula and questions the correctness of their answer based on feedback received. Some participants discuss the significance of the negative sign in the context of work done and whether the question requires the magnitude or the signed value. Others raise questions about the units specified in the problem.

Discussion Status

The discussion is ongoing, with participants providing differing perspectives on the necessity of the negative sign in the work calculation. There is no explicit consensus on the correct approach, and the original poster expresses confusion over the feedback received regarding their answer.

Contextual Notes

Participants note the potential ambiguity in the problem regarding the required units and the interpretation of the work's sign. The original poster indicates that they have not received further clarification on these aspects.

rperez1
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Homework Statement



How much work is required to stop an electron (m=9.11×10−31kg) which is moving with a speed of 1.40×10^6 m/s ?

2. Homework Equations

The Attempt at a Solution



E.g a particle has KE=10J. The work that must be done on it to stop it is -10J.

So work out the kinetic energy of the electron(½mv²) and put a minus sign in front. I get -8.93x10⁻¹⁹ J.but when i answer the question it says i am wrong? can someone please help me
 
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No need of minus sign dear.
Minus sign represents the direction. But question don's ask a direction. So remove the minus sign. Then it'll be okay.:smile:
 
rperez1 said:
E.g a particle has KE=10J. The work that must be done on it to stop it is -10J.
Technically, you are correct: The work done must be negative. But apparently they just want the magnitude of the work, not the sign.
 
Doc Al said:
Technically, you are correct: The work done must be negative. But apparently they just want the magnitude of the work, not the sign.
it still says incorrect when i take out the negative which makes no sense bc i have no other way to get another answer.
 
Jimmy Moriaty said:
No need of minus sign dear.
Minus sign represents the direction. But question don's ask a direction. So remove the minus sign. Then it'll be okay.:smile:
it still continues to say that it is incorrect, which makes no sense bc i know i did it correctly, i have no other way to get another answer. i don't know what is wrong with my answer.
 
Do they specify the units they want you to use? (Joules makes sense, but there are other units.)
 

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