Angular velocity, can someone help?

[knowledgerich]

Homework Statement

a laboratory centrifuge has rotor radius (from center of rotor to sample) of 12.0 cm and typically spins at a rate of 2000 rpm. When switched off, it turns through 50.0 revolutions in coming to rest. Find the value of its average angular acceleration.

Homework Equations

The Attempt at a Solution

so far I only turned the rpm to radians/s which is the angular velocity but I wasn't sure what to do next

 

[tiny-tim]

welcome to pf!

hi knowledgerich! welcome to pf!

a laboratory centrifuge has rotor radius (from center of rotor to sample) of 12.0 cm and typically spins at a rate of 2000 rpm. When switched off, it turns through 50.0 revolutions in coming to rest. Find the value of its average angular acceleration.
…
so far I only turned the rpm to radians/s which is the angular velocity but I wasn't sure what to do next

you have initial speed, final speed, and total distance, and the question asks for acceleration

sooo … just use one of the standard constant acceleration equations (but using angle instead of distance)

 

[knowledgerich]

is the radius used in this equation? I came up with (-33^2 rad/s)/(2*100π) = -3.5 rad/s^2

 

[haruspex]

is the radius used in this equation? I came up with (-33^2 rad/s)/(2*100π) = -3.5 rad/s^2

No, I think the radius was given you to confuse you. (There ought to be more questions like that IMO.)
What are the units of the '33'?

 

[tiny-tim]

is the radius used in this equation?

the radius would only be needed if they gave you the tangential (linear) speed instead of the angular speed …

eg if they said a wire was coming off the wheel at so-many metres per second ​