Question

4. Find the moment of inertia of a uniform rectangle of side 2a and 2b and mass
M about an axis along one edge of length 2b.

Answer 1

So you need to calculate this from first principles?

Answer 2

or can you use the Parallel Axis Theorem?

Answer 3

im familiar with parallel axis theorem..=) but i dont know how to do..

Answer 4

What do you believe you are supposed to do here?
a) calculate the moment of inertia from first principles, calculating an integral \( \int r \ dm \)
b) use the moment of inertia of a rectangle with an axis through the center of the rectangle that you know already together with the parallel axis theorem

Answer 5

@_@ a maybe..

Answer 6

All right.

Well, an element of area, dA has mass of dm = (m/4ab) dA because the total area is 4ab. So far so good?

Answer 7

is that the axis is like this..?

Answer 8

No, it says the axis is along the edge that is 2b long

Answer 9

james yes i get that..

Answer 10

Hey, how about find the centroid, use parallel axis, the MOI of a rectangle is bh^3/12?

Answer 11

@arctic, that's option (b). fasha has said explicitly we're using option (a).

Answer 12

wait2..how is the axis actually?

Answer 13

Oh ok!