physics
posted by Bruce on .
A uniform brass disk of radius R and mass M with a moment of inertia I about its cylindrical axis of symmetry is at a temperature T = 45 °C. Determine the fractional change in its moment of inertia if it is heated to a temperature of 125 °C. (The linear expansion coefficient for brass is 1.90 105 °C−1.)
I tried finding the change in volume and using that ratio, but it isn't correct. Im not sure what the best approach is. Thank you for any suggestions!

You have been given the linear expansion coefficient  find increase in radius R and then find the disk's MI.

ΔR=R•α•ΔT=R•1.9•10^5•(12545)=0.00152•R
R1=R+0.00152•R =R•1.001525
I=mR²/2
I1= mR1²/2= mR²•1.001525²/2=1.003• mR²/2=1.003•I
I1/I=1.003 or
I/I1=1/1.003=0.997 
thank you!