# Circular motion and gravity help

1. Jun 8, 2013

### katiegerster

1. The problem statement, all variables and given/known data

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.

2. Relevant equations

T=mg

3. The attempt at a solution

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

2. Jun 8, 2013

### 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.

3. Jun 8, 2013

### katiegerster

the second question is just conceptual so i had hoped it wouldnt make things to confusing, im sorry

4. Jun 8, 2013

### voko

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

5. Jun 8, 2013

### katiegerster

i know, its because i dont even know what equation to use for it, no one can seem to figure out how to solve it...

6. Jun 8, 2013

### voko

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