Rotational kinetic energy of particles

[SpecialOps0]

Homework Statement

The four particles shown below are connected by rigid rods of negligible mass where y1 = 6.60 m. The origin is at the center of the rectangle. The system rotates in the xy plane about the z axis with an angular speed of 5.40 rad/s.
http://www.webassign.net/serpse8/10-p-025-alt.gif

(a) Calculate the moment of inertia of the system about the z axis.

(b) Calculate the rotational kinetic energy of the system.

Homework Equations

I = kg*m^2
I= sum of all mr^2

K=.5Iw^2

The Attempt at a Solution

5.4/2=2.7
2.7^2=7.29+2^2=11.29
11.29 = A
2A+2A+3A+4A = 124.19 kgm^2
=120B)
.5*124.19*5.4^2 rad/s = 1810.6902
=1810JFor some reason when I enter them in they are wrong. On the practice problem it has it as two sig figs so that's what I used in the answer and it's incorrect. Am I doing something wrong?

 

[ashishsinghal]

I am not able to get what you are trying to do. Please explain your method. What is A?

 

[SammyS]

y₁ = 6.60 m.

What does 5.4 rad/s have to do with the distance the particles are from the z-axis?