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hitspace
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Homework Statement
If we multiply all the design dimensions of an object by a scaling factor (f), its volume and mass will be multiplied by f^3. a) By what factor will its moment of inertia be multiplied? b) IF a 1/48 scale model has rotational kinetic energy of 2.5 Joules, what will be the kinetic energy for the full-scale object of the same material rotating at the same angular velocity?
Homework Equations
KE = 1/2 (I) w^2
I_Disk = (1/2) M (r^2)
The Attempt at a Solution
Wasn't really sure how to approach this problem as my understanding of moment of inertia, is that it changes according to the dimensions of an object. I decided to try this problem anyway assuming a solid disk spun about the central axis. I attempted part b) wherein I set up the equations as follows
if 2.5 = .5 [ .5 (M)r^2 ] w^2
then .5 [ .5 (48M)(48r)^2 ] w^2 = 48^3 {.5 [ .5 (M)r^2 ] w^2 }
I got the answer 2.5 * 48^3 = 2.76 E6 Joules.
My solutions manual says I should have multiplied by 48^5 instead of to the third power.
Any ideas?