Circular motion and gravity help

[katiegerster]

Homework Statement

1. The mass of a star is 1.830×1031 kg and it performs one rotation in 37.30 days. Find its new period (in days) if the diameter suddenly shrinks to 0.850 times its present size. Assume a uniform mass distribution before and after.

2. A pulley with mass Mp and a radius Rp is attached to the ceiling, in a gravity field of 9.81 m/s2 and rotates with no friction about its pivot. Mass M2 is larger than mass m1. The quantities Tn and g are magnitudes. Choices: true, false, greater than, less than, or equal to.

The C.M. of Mp+M1+M2 does not accelerate.
T1 is ... T2
m1g + M2g + Mpg is ... T3.
T3 is ... T1 + T2
T2 is ... M2g.
The magnitude of the acceleration of M2 is ... that of m1.

Homework Equations

T=mg

The Attempt at a Solution

do not know how to go about solving either of these :(

 

[voko]

Don't post two different problems in one thread. I am not sure this is strictly against the rules, but it makes things very confusing.

 

[katiegerster]

the second question is just conceptual so i had hoped it wouldn't make things to confusing, I am sorry

 

[voko]

It may be, but you ignored the template requirements for the first question.

 

[katiegerster]

i know, its because i don't even know what equation to use for it, no one can seem to figure out how to solve it...

 

[voko]

What properties of rotating bodies do you know about, especially those that are conserved?