- #1

jisbon

- 476

- 30

- Homework Statement
- Calculate moment of inertia of a 2d plane rotating about x axis. Mass per unit area of plate = ##1.4g/cm^2## , total mass = 25.2g

- Relevant Equations
- ##I=\int y^2 dm##

I've attempted this question, but the answer seems to be incorrect. Here's my workings:

##I=\int y^2 dm## - standard equation

##dM = \mu * dy * x## - take small slice and find mass of it

##x = 4y-16## - convert equation in terms of x to sub in later

##dM = \mu * dy * 4y-16##

##I=\int y^2 \mu * dy * 4y-16##

##I=\mu\int y^2(4y-16) dy##

##I=\mu\int 4y^3-16y^2 dy##

##I=\mu \int_{0}^{3} 4y^3-16y^2 dy## = 12.6, which is not the answer.

Any clues why?