How much work is required to stop an electron

[rperez1]

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

 

[Jimmy Moriaty]

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.

 

[Doc Al]

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.

 

[rperez1]

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.

 

[rperez1]

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.

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.

 

[Doc Al]

Do they specify the units they want you to use? (Joules makes sense, but there are other units.)