Angular acceleration of a skater

[brad sue]

Hi,
I need help with the following problem.

A skater does a pirouette at the rate of 2.0 rev / second and then stop within 3/4 rev. Assume that the angular decceleration is constant and calculate its magnitude.

I tried to compute it but I found -18 rad/s².
BUt the textbook gives -17 rad/s².
Please can someone help me with this problem?

Thank you
B

 

[andrevdh]

brad sue,
use
$$\omega^2 \ = \ {\omega^2}_o \ + \ 2\alpha \ \Delta\theta$$
The rotational equivalent of
$$v^2 \ = \ {v^2}_o \ + \ 2as$$

 

[Astronuc]

What formula did you use to compute 18 rad/s²?

What is the angular analogy to v² = v_o² + 2ax?

The 17 rad/s would be rounded.

 

[brad sue]

What formula did you use to compute 18 rad/s²?
What is the angular analogy to v² = v_o² + 2ax?
The 17 rad/s would be rounded.

Yes the -17 has been rounded.
Thank you very much you all..

B