I've ran aground on my physics 4a homework. Consider a solid disk of mass M=15.6kg and areal density =Dx3. Determine the value D if the radius of the disk is 0.25m. I solved the problem before it: (a)Consider a two meterstick of mass M=8.2kg and linear density =Cx5. Determine the value C. by taking the intergral of the linear density and setting it equal to the mass and plugging in 2 meters for the x and solving for C. Changing the object to a disk from a meter stick somehow destroys the problem from me and I can't figure out what to do to get it to work. I've tried finding area pi(r)^2 using the radius that gave, and i've tried circumferance 2pi(r). What I'm I missing?