- #1

EVriderDK

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## Homework Statement

A bridge takes 2 minutes to open up fully from 0 to 80 degrees. The first 20 degrees it is accelerating, and the last 60 degrees it is traveling with even velocity.

I will have to find acceleration for the first 20 degrees and angular velocity for the last 60 degrees.

http://peecee.dk/upload/view/357409 Illustration.

## The Attempt at a Solution

I have tried setting up three equations with three unknowns:

http://peecee.dk/upload/view/357410

I have tried isolating a in the first two equations, and then put 1=2. Then isolating ω in this new equation, and replacing this with the ω in the third equation. Then i isolate t, and get 48 second. This gives the correct answer to the acelleration, but i don't know why. Can you help?

Is there other way to do it maybe?

Thank you in advance.

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