Rotational Motion around a Fixed Axis

[Ollie359]

The drawing shows the top view of two doors. The doors are uniform and identical. Door A rotates about an axis through its left edge, and door B rotates about an axis through the center. The same force is applied perpendicular to each door at its right edge, and the force remains perpendicular as the door turns. Starting from rest, door A rotates through a certain angle in 3.00 s. How long does it take door B to rotate through the same angle?

 

[andrewchang]

what work have you done on the problem?

 

[Ollie359]

I haven't.. I have no idea where to start! :(

 

[Ollie359]

I've tried different equations. But there is an answer in the back of the book.. and everything that I try to do doesn't come out to be that answer. I'm kinda stumpped on what equation to use since there is only one number given in the problem...

 

[lightgrav]

It's a question about rotation ... relevant ideas are :
angular velocity, Torque, anglar acceleration, Moment of (rotational) Inertia, angular momentum.

Which are different for these doors? Different by what factor?
(double? half?)

 

[Ollie359]

its different by half right? since the axis is in the middle instead of outside. I got that but I'm not sure what that pertains too..