Angular acceleration and angular velocity

[John78]

Homework Statement

Calculate the angular acceleration and angular velocity of a 4 kg object rotating in a circle of 3 m radius in a time of 6 s.

Homework Equations

The Attempt at a Solution

Angular acceleration = ω2*r

C=2∏r= 2*3.14*3=18.84
360°/57.3°=6.28 rad/s
6.28/6= 2.09 rad/sec

Angular acceleration= (2.09)2*3=12.54??


Angular velocity= angular displacement/time ?



I just want to check whether my working is correct or not.

 

[emailanmol]

Nope.Its not right.

Remember, angular acceleration is dw/dt.

The acceleration w^2*r is centripetal accelwration.

Infact writing angular acceleration as w^2*r is dimemsionally inconsistent.


As nothing had been told about how w changes with time nothing can be said about angular acceleration.

In such cases w is assumed to be constant making angular acceleration 0

 

[John78]

angular acceleration = 0


what about angular velocity?

 

[tiny-tim]

Hi John78!

angular acceleration = 0

Correct.

what about angular velocity?

Your formula …

Angular velocity= angular displacement/time

… is fine