# Homework Help: What is the angular acceleration of an arm

1. Apr 13, 2017

### Dusty912

1. The problem statement, all variables and given/known data
what is the angular acceleration of the arm when theta equals 45 degrees.
v=2 m/s
picture is attached
2. Relevant equations
law of sites
law of cosines

3. The attempt at a solution

so I used the law of sines to resolve side r as being 579.555 mm
now I now I need to take time derivative of theta somewhere using law of cosine or sines but I'm not really sure which one. also I don't know how to relate the 2 m/s to the problem

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2. Apr 14, 2017

### Orodruin

Staff Emeritus
Hint: The velocity is telling you how fast the long side is increasing.

3. Apr 14, 2017

### Dr.D

Write the vector expression describing the closed loop. Solve this for the angular orientation of the arm (it will appear in the vector components). Take the time derivative of that result.