M1 problem help!

a string passes over a rough cylindrical rail, object of mass 10kg and 12kg attached to the ends gang vertically on either side. because of friction between the string and the rail, when the objects are in motion the tension in the string on the descending side is twice the tension on the ascending side, find the acceleration of the system. the answer is 0ms^-2
idk how they did that please help and tell me how they did it

Reply 1

Haesights

6

Firstly, have you attempted to draw a diagram with all forces labelled?

Reply 2

ghostwalker

17

Original post by swagadon

...

Can you provide a scan of the question, or a link to it, so we can see the exact wording.

I suspect it's the case of, IF the masses are in motion then one tension is twice the other, and this leads to a contradiction, and so we conclude that the masses are not in motion, and acceleration is zero.

But, I'd really like to see the original question.

A similar thread.

Reply 3

swagadon

OP

7

Original post by ghostwalker

Can you provide a scan of the question, or a link to it, so we can see the exact wording.

I suspect it's the case of, IF the masses are in motion then one tension is twice the other, and this leads to a contradiction, and so we conclude that the masses are not in motion, and acceleration is zero.

But, I'd really like to see the original question.

A similar thread.

yeah it was the exact same question on the similar thread i just didnt put the a b c cuz im lazy haha, but i was stuck on c) do you know how to do it? its really stressing me out haha

Reply 4

boner in jeans

Original post by swagadon

yeah it was the exact same question on the similar thread i just didnt put the a b c cuz im lazy haha, but i was stuck on c) do you know how to do it? its really stressing me out haha

exact same method as in the other thread

solve with simultaneous equations

Reply 5

TenOfThem

18

So, as ghostwalker says

When m=12 this leads to a contradiction

Therefore there is no motion taking place

Reply 6

swagadon

OP

7

Original post by TenOfThem

So, as ghostwalker says

When m=12 this leads to a contradiction

Therefore there is no motion taking place

yeah but how would you know that theres no motion? it doesnt tell you,andyou wouldnt know the answer

Reply 7

TenOfThem

18

Original post by swagadon

yeah but how would you know that theres no motion? it doesnt tell you,andyou wouldnt know the answer

It says WHEN in motion ... blah blah blah

Since the blah blah blah cannot be true the is no motion

So it does tell you

Reply 8

ghostwalker

17

Original post by swagadon

yeah but how would you know that theres no motion? it doesnt tell you,andyou wouldnt know the answer

You start by assuming that there is motion. Note that the question says that one tension is twice the other WHEN there is motion. Show that this leads to a contradiction (in this case the acceleration works out as negative). And therefore you can conclude that there is no motion.

It's an unusual question for A-level.

Reply 9

TenOfThem

18

Original post by ghostwalker

It's an unusual question for A-level.

It certainly is.

I do not think it is an actual A Level exam question.

Reply 10

swagadon

OP

7

Original post by ghostwalker

You start by assuming that there is motion. Note that the question says that one tension is twice the other WHEN there is motion. Show that this leads to a contradiction (in this case the acceleration works out as negative). And therefore you can conclude that there is no motion.

It's an unusual question for A-level.

ahhh i see,how did you know that? haha is it in any of the other mechanics modules?