Atwood Clarification: Tensions & Masses

[Vanessa23]

Homework Statement

In a system where the atwood is suspended by a massless string with T3 and M1>m2. M1 is lower than m2. Relate Tensions and masses if it is frictionless, pulley and string are massless.

Homework Equations

T1 is tension in string holding M1; T2 is tension in string holding M2.

The Attempt at a Solution

I believe that when there is no acceleration:
T3=M1+m2
T1=M1g
T2=m2g
but shouldn't T1=T2?

when there is acceleration then the system CM does not change, but the CM of M1 and m2 is lowered since M1 falls lower. Or will it stay the same since M1 is already lower than m2?

also, since T3 is being taken into account (which I can't find an example of), will it have a negative tension compared with the other tensions?

 

[Kurdt]

You may find the following page useful in clarifying your questions:

http://hyperphysics.phy-astr.gsu.edu/hbase/atwd.html

Have a look and feel free to ask any more questions.

 

[PhanthomJay]

Homework Statement

In a system where the atwood is suspended by a massless string with T3 and M1>m2. M1 is lower than m2. Relate Tensions and masses if it is frictionless, pulley and string are massless.

Homework Equations

T1 is tension in string holding M1; T2 is tension in string holding M2.

The Attempt at a Solution

I believe that when there is no acceleration:
T3=M1+m2
T1=M1g
T2=m2g
but shouldn't T1=T2?

Yes, good observation. So what does that tell you about the system when M1 and m2 are not equal?

when there is acceleration then the system CM does not change,

what makes you say that?

but the CM of M1 and m2 is lowered since M1 falls lower. Or will it stay the same since M1 is already lower than m2?

the CM will lower

also, since T3 is being taken into account (which I can't find an example of), will it have a negative tension compared with the other tensions?

there's no such thing as a negative tension. Once you solve for the string tension around the pulley (where you must note that T1=T2 for strings wrapped around massless frictionless pulleys), you can find T3 with a FBD of the massless, at rest pulley.

 

[Vanessa23]

So if it is true that in this situation T3=M1+m2, then why is it that T3 is less than M1+m2+the mass of the pulley (when it isn't massless)?
and why is T1 greater than T2?
and T3 greater than T1+T2?