- #1

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter Istiak
- Start date

- #1

- #2

berkeman

Mentor

- 63,642

- 14,755

- #3

- 5,695

- 2,473

The attachment explains the problem setup but then it offers some choices but it doesn't mention what is the question. It looks like it is asking what is the total potential energy of the system.

And besides that, on your own work you seem to work towards finding the equilibrium position for charge q. Is that what you trying to find?

- #4

Istiak

- 158

- 10

Yes! It is. That's what I wrote. I was trying to find that value. Potential energy depends on the X²

The attachment explains the problem setup but then it offers some choices but it doesn't mention what is the question. It looks like it is asking what is the total potential energy of the system.

And besides that, on your own work you seem to work towards finding the equilibrium position for charge q. Is that what you trying to find?

- #5

AF Fardin

- 7

- 1

Yep

- #6

- 5,695

- 2,473

At start you write ##F=qE## or ##k''x=qE##

But after some point you write ##F'+F=qE##

And later ##F''+F'+F=qE##

only one case can be true, or I just don't understand something here.

- #7

berkeman

Mentor

- 63,642

- 14,755

Yep

I was about to delete your reply as unnecessary, but when I checked your previous posting history, I see that you posted about a similar/same problem earlier today and the post was deleted because you showed no effort. Your attachment is added below; are you and @Istiakshovon in the same class?

- #8

Steve4Physics

Homework Helper

Gold Member

- 1,465

- 1,273

“

The question is apparently

“

That’s not a homework statement. You need to give the complete question.

The equation is wrong. Maybe you mean E = kq/r^2 or F = kq₁q₂/r^2. However, neither of these equations is relevant to your question!

Like @Delta2, I too I can’t understand your solution attempt.

You have ignored @berkeman's post (#2). Is there a reason? I don’t think you will get help unless you at least post the

- #9

Istiak

- 158

- 10

Actually, he was new to the community. He didn't understand how the community works. He wasn't familiar with these tools. So, he told me to create new thread here cause, I had talked about the community to him. Then, I had posted it. I hope you understood. I know that "Yep" comment is unnecessary. So, you can delete that. He doesn't know code of conduct of the community either. I haven't read COC also.I was about to delete your reply as unnecessary, but when I checked your previous posting history, I see that you posted about a similar/same problem earlier today and the post was deleted because you showed no effort. Your attachment is added below; are you and @Istiakshovon in the same class?

View attachment 284973

- #10

Istiak

- 158

- 10

As I mentioned in my previous reply that this question is not mine. It's another person's. I didn't have much more time to look at his works. So, that what I simply understood without reading answer and question, I had just added that. As I said I didn't have much more time, that's why I added unnecessary **Homework Statement**

“Title:Find the electric field”

The question is apparentlynotabout finding the electric field!

“Homework Statement:Electric field”

That’s not a homework statement. You need to give the complete question.

Relevant Equations:F = kq/r^2

The equation is wrong. Maybe you mean E = kq/r^2 or F = kq₁q₂/r^2. However, neither of these equations is relevant to your question!

Like @Delta2, I too I can’t understand your solution attempt.

You have ignored @berkeman's post (#2). Is there a reason? I don’t think you will get help unless you at least post thecompletequestion, as requested. (I can possibly guess what the question is but I might be wrong.)

- #11

Istiak

- 158

- 10

- #12

- 5,695

- 2,473

No it isn't bug, the forum software doesn't let you edit the post a few hours after it was initially posted.I was trying to edit my question. Unfortunately, there's no edit button. Is it bug?

- #13

Istiak

- 158

- 10

So, How can I edit Homework Statement?No it isn't bug, the forum software doesn't let you edit the post a few hours after it was initially posted.

- #14

- #15

Istiak

- 158

- 10

https://www.physicsforums.com/attachments/e4e2c5e8-5062-4bbf-94a7-55bbd56e393c-jpeg.284961/

- #16

- 5,695

- 2,473

Ok fine for the description of the problem setup, but you didn't tell us what is the question asked. Is it "Find the equilibrium position for mass m"?Homework Statement:The second mass (m) also carries a charge q while the mass M is uncharged and made of an insulator. The masses are allowed to move only along the horizontal direction. The distance between the plates A and B as shown in the figure is fixed. Moreover there is a horizontal uniform electric field E that runs between A and B plates and points from left to right.

https://www.physicsforums.com/attachments/e4e2c5e8-5062-4bbf-94a7-55bbd56e393c-jpeg.284961/

- #17

Istiak

- 158

- 10

I am forwarding it to @AFFardin. @AFFardin Reply to him using the reply button to his replyOk fine for the description of the problem setup, but you didn't tell us what is the question asked Is it "Find the equilibrium position for mass m"?

- #18

AF Fardin

- 7

- 1

F"+F'+F=qE

At start you write ##F=qE## or ##k''x=qE##

But after some point you write ##F'+F=qE##

And later ##F''+F'+F=qE##

only one case can be true, or I just don't understand something here.

This is true I think !

- #19

AF Fardin

- 7

- 1

At First, I wasn't sure about it!F"+F'+F=qE

This is true I think !

I was trying and thinking with some roughs!

And that's what made you confused. My final thought is this (F"+F'+F=qE).

Still don't know that my approach is correct or wrong!

- #20

AF Fardin

- 7

- 1

YesI was about to delete your reply as unnecessary, but when I checked your previous posting history, I see that you posted about a similar/same problem earlier today and the post was deleted because you showed no effort. Your attachment is added below; are you and @Istiakshovon in the same class?

View attachment 284973

- #21

AF Fardin

- 7

- 1

[6/25, 09:49] AF_Fardin: Both X and YOk fine for the description of the problem setup, but you didn't tell us what is the question asked. Is it "Find the equilibrium position for mass m"?

[6/25, 09:49] AF_Fardin: Means for both masses

- #22

- 5,695

- 2,473

- #23

- 5,695

- 2,473

$$Kx-K'y=0$$

$$K'y+Eq-K''z=0$$

$$x+y+z=L$$

The first equation is from the equilibrium condition on mass M, the second from the equilibrium condition on mass m, and the third is self explanatory

P.S We assume that the springs have zero natural length.

- #24

AF Fardin

- 7

- 1

Wow thank you !

$$Kx-K'y=0$$

$$K'y+Eq-K''z=0$$

$$x+y+z=L$$

The first equation is from the equilibrium condition on mass M, the second from the equilibrium condition on mass m, and the third is self explanatory

P.S We assume that the springs have zero natural length.

Could you please explain it explicitly for me?

- #25

Istiak

- 158

- 10

But, actually your approximation doesn't match with any option. What should I do next (with this equation)?

$$Kx-K'y=0$$

$$K'y+Eq-K''z=0$$

$$x+y+z=L$$

The first equation is from the equilibrium condition on mass M, the second from the equilibrium condition on mass m, and the third is self explanatory

P.S We assume that the springs have zero natural length.

- #26

- 5,695

- 2,473

Could be that my equations are wrong. Can you tell me what are the available options, maybe i can do some reverse engineering of some sort ...But, actually your approximation doesn't match with any option. What should I do next (with this equation)?

- #27

Istiak

- 158

- 10

Look at this picture..Could be that my equations are wrong. Can you tell me what are the available options, maybe i can do some reverse engineering of some sort ...

1.

$$\frac{1}{2} kx^2 + \frac{1}{2} ky^2 - qEY$$

2.

$$\frac{1}{2} kx^2 + \frac{1}{2} ky^2 - qE(Y+X) + \frac{1}{2} K''(L-x-y)^2$$

3.

$$\frac{1}{2}kx^2+\frac{1}{2}ky^2-qEY+\frac{1}{2} (L-x-y)^2$$

4.

$$\frac{1}{2}kx^2+\frac{1}{2}ky^2-qE(x+y)$$

5.

$$\frac{1}{2}kx^2+\frac{1}{2}ky^2+\frac{1}{2}k''(L-x-y)^2$$

Unfortunately, MathJax isn't working. I had tried with "####" also. I had tried as we use in SE or, CD

Last edited:

- #28

- 5,695

- 2,473

- #29

Steve4Physics

Homework Helper

Gold Member

- 1,465

- 1,273

My apologies. You are just trying to help someone out. Well done for that!As I mentioned in my previous reply that this question is not mine. It's another person's. I didn't have much more time to look at his works. So, that what I simply understood without reading answer and question, I had just added that. As I said I didn't have much more time, that's why I added unnecessary **Homework Statement**

But note, even after 28 posts, we do not know what the actual question is! If at all possible, post the complete question. We shouldn't have to make any assumptions such as "the springs have zero natural length" (@Delta , Post #23); all essential information should be included as part of the question.

- #30

Istiak

- 158

- 10

Actually, that was like an exam (Olympiad). My friend had joined to that. Then, he thought his work isn't correct that's why he told me to post it here.

And, no matter what I choose the site won't show correct answer. That's why I/he wants to know the approximation/answer.

- #31

Istiak

- 158

- 10

Actually, I had gave the whole question and, figure in following picture. You can see the whole question in the image also.My apologies. You are just trying to help someone out. Well done for that!

But note, even after 28 posts, we do not know what the actual question is! If at all possible, post the complete question. We shouldn't have to make any assumptions such as "the springs have zero natural length" (@Delta , Post #23); all essential information should be included as part of the question.

- #32

- 5,695

- 2,473

Actually I can't see what the question is. I can read only the description of the system. What I canActually, I had gave the whole question and, figure in following picture. You can see the whole question in the image also.

- #33

Istiak

- 158

- 10

Yes! You got the question..Actually I can't see what the question is. I can read only the description of the system. What I canguessis asking (judging from the available options) is "What is the total potential energy of the system?"

- #34

- 5,695

- 2,473

The correct option according to my opinion is option 2.Yes! You got the question..

- #35

Steve4Physics

Homework Helper

Gold Member

- 1,465

- 1,273

I'm not surprised!And, no matter what I choose the site won't show correct answer.

@Delta has (I believe correctly) guessed that the question is 'What is the potential energy?'. But original question does not even mention potential energy!

The meaning of distances X and Y is very unclear. The question-wording does not mention X or Y. And the diagram in Post#1 does not show X and Y properly. (An accurate diagram showing the meanings of X and Y would help a lot.)

Assuming you have posted the full question, then it seems that whoever wrote the original question made a

Share:

- Last Post

- Replies
- 2

- Views
- 186

- Replies
- 10

- Views
- 87

- Last Post

- Replies
- 6

- Views
- 389

- Replies
- 4

- Views
- 271

- Last Post

- Replies
- 4

- Views
- 252

- Last Post

- Replies
- 14

- Views
- 622

- Last Post

- Replies
- 9

- Views
- 361

- Last Post

- Replies
- 1

- Views
- 254

- Replies
- 14

- Views
- 454

- Replies
- 6

- Views
- 368