Angular deceleration of a circular saw blade

[Tikki]

Homework Statement

If a circular saw blade is spinning at a rate of 6.57 revolutions per second, what is the magnitude of the (constant) angular acceleration that needs to be applied on the saw blade to bring it to rest in 17.2 revolutions?

Relevant Equations

theta = no of revs * 2pi
w^2=2a(theta)

I tried the formula I showed up there but got 0.399 instead of 7.88rad/s^2.

 

[kuruman]

What number did you use for w?

 

[Tikki]

What number did you use for w?

6.57rads/s

 

[Tikki]

6.57rads/s

wait a min?

 

[kuruman]

wait a min?

Yup, it is given in revolutions per second.