- #1

Mikkel

- 27

- 1

## Homework Statement

Hello!

I apologize for my poor setup, first post.

I am given a system of two rods, hope you can see my image.http://file:///C:/Users/Mikkel/Downloads/Mek2_exam_Jan2016_final.pdf

One along the x-axis with mass = 2m and length = 2l

Another perpendicular with the other with mass = m and length = l

The system rotate around a point O

Find the angular velocity at the point when the systems longest rod is vertical.

## Homework Equations

I have calculated the center of mass rcm = ( (4/3)*l , (1/6)*l )

and the distance from pivot point to the center of mass = (1/6) * sqrt(65) * l

Also the moment of inertia for the system = 7*m*l

^{2}

## The Attempt at a Solution

I have tried the following so far:

I tried to use conservation of energy to solve it:

m*g*h + 0 = 0 + (1/2)*I*w

^{2}

I am thinking that I have a total of mass 3

and the height has to be the x-coordinate for center of mass (I think this is where I might be wrong?)

3*m*g*(4/3)*l = (1/2)*7*m*l

^{2}* ω

^{2}

after a bit of calculations...

ω = sqrt((8*g)/(7*l))

However my facit says ω = sqrt((9*g)/(7*l))

I can't figure it out!

Appreciate any tips ! :)

#### Attachments

Last edited by a moderator: