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# Mechanics Understanding Help watch

1. (Original post by Smaug123)
If you mean "the tension in both chunks of the string": it must be, because the string is inextensible. Suppose the tension were different at two different points on the string. Then there would be a net force on a point in between those points, so that in-between point would have to be moving (because things move when a force is applied to them). But in this problem, the string is stationary.

The idea is that "if we look at a perpendicular cross-section of the string, we can't determine how far along the string we took the cross-section". Is that idea intuitively clear to you?
Wrong! The tensions are the same because the string is threaded through a SMOOTH BEAD.
2. (Original post by TARS)
Wrong! The tensions are the same because the string is threaded through a SMOOTH BEAD.
That's my point. I assume for contradiction that the tensions are different. I then derive a contradiction.
3. (Original post by ghostwalker)
If the car is breaking, there may be tension in the rope, but there can't be thrust, a rope doesn't support compression.

Can't make sense of that as it stands.
https://3b0a7b1bc87f5381e60f8f717510...%20Edexcel.pdf

Q7... When breaking, there's no tension, but there's thrust... So when do I consider thrust and when do I know when to include thrust or tension when resolving?

Posted from TSR Mobile
4. (Original post by ps1265A)
https://3b0a7b1bc87f5381e60f8f717510...%20Edexcel.pdf

Q7... When breaking, there's no tension, but there's thrust... So when do I consider thrust and when do I know when to include thrust or tension when resolving?

Posted from TSR Mobile
Can't give you a list of all cases off the top of my head. It's going to depend on the question. And there really isn't a lot of point in asking me this sort of question. I did my A-levels decades ago, and I'm not a teacher.

You really don't want to be looking for this sort of a list anyway. Understand the basics, Newtons Laws, resolving forces, resultant forces, etc, and apply to each situation as appropriate.
5. (Original post by ps1265A)
https://3b0a7b1bc87f5381e60f8f717510...%20Edexcel.pdf

Q7... When breaking, there's no tension, but there's thrust... So when do I consider thrust and when do I know when to include thrust or tension when resolving?

Posted from TSR Mobile
There is thrust in the rod as it is being squashed. If it helps you visualise it push the two ends of your pen together. The outward force that stops you from breaking it is thrust.
6. (Original post by ghostwalker)
Can't give you a list of all cases off the top of my head. It's going to depend on the question. And there really isn't a lot of point in asking me this sort of question. I did my A-levels decades ago, and I'm not a teacher.

You really don't want to be looking for this sort of a list anyway. Understand the basics, Newtons Laws, resolving forces, resultant forces, etc, and apply to each situation as appropriate.
Alright thanks!

https://3b0a7b1bc87f5381e60f8f717510...%20Edexcel.pdf

For Q2, I made the following triangle to solve for p; I got the right answer, but it wasn't an exact value... I was just wondering if the method use is correct?

I understand that there's an easier way to go about it
7. (Original post by ps1265A)
Alright thanks!

https://3b0a7b1bc87f5381e60f8f717510...%20Edexcel.pdf

For Q2, I made the following triangle to solve for p; I got the right answer, but it wasn't an exact value... I was just wondering if the method use is correct?

I understand that there's an easier way to go about it
Yes that method checks out, you didn't get an exact value due to rounding. I'm assuming you're overcomplicating it for sake of practice
8. (Original post by KMan98)
Yes that method checks out, you didn't get an exact value due to rounding. I'm assuming you're overcomplicating it for sake of practice
Haha, yes! Thanks!

Could you help me out here http://www.thestudentroom.co.uk/show...3#post56464553
9. (Original post by ghostwalker)
Can't give you a list of all cases off the top of my head. It's going to depend on the question. And there really isn't a lot of point in asking me this sort of question. I did my A-levels decades ago, and I'm not a teacher.

You really don't want to be looking for this sort of a list anyway. Understand the basics, Newtons Laws, resolving forces, resultant forces, etc, and apply to each situation as appropriate.
http://www.thestudentroom.co.uk/show...3#post56466893
Could you help me with this thread?

https://3b0a7b1bc87f5381e60f8f717510...%20Edexcel.pdf

And for Q6, can I resolve horizontally and vertically?
10. (Original post by ps1265A)
http://www.thestudentroom.co.uk/show...3#post56466893
Could you help me with this thread?

https://3b0a7b1bc87f5381e60f8f717510...%20Edexcel.pdf

And for Q6, can I resolve horizontally and vertically?
Yes, you can resolve and then use pythag or set up a triangle of forces.

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