Mass, Moments and Center of Mass

[dimpledur]

Homework Statement

A square plate with edge a cm and areal density kr g/cm^2, where r is the distance (in centimetres) from P to one of the diagnals of the square.

Find the mass.

The Attempt at a Solution

I know my diagram is wrong, and I know what the correct one looks like. However, I do not see how my diagram does not work... All of the diagnals meet at the centre which in my diagram is the origin. Hence, and radius extends from all the diagnals to position P.

Any ideas?

 

[tiny-tim]

hi dimpledur!

the diagonal is one of the two lines from one corner to the opposite corner

 

[dimpledur]

Yeah, so in my diagram r extends from both diagnals, does it not? I'll provide another picture.

 

[tiny-tim]

yes, so choose one of the diagonals, as in the question …

… where r is the distance (in centimetres) from P to one of the diagnals of the square.

 

[dimpledur]

Here, r extends from the very center where the diagnals meet, and hence touches both.. hmm

 

[dimpledur]

yes, so choose one of the diagonals, as in the question …

So the easiest way to appreach this would be to rotate the square such that r is perpendicular to the diagnal of the square?

 

[tiny-tim]

Here, r extends from the very center …

erm, noooo …

r is perpendicular to one diagonal

 

[dimpledur]

Okay, thanks.