Dynamics question: Angular Velocity/kinematics

[GaryTravis]

A piece of stone of mass m is rotating at constant angular speed ω in the vertical plane about the point O as shown in the figure. A rope of length R connects the ball to O. If the rope breaks when the stone is at A, calculate how long it takes before the stone falls back to the same level (y=0). Pick the closest answer in seconds.

http://huygens.zones.eait.uq.edu.au/courses/engg1400/pic/ball_on_a_rope.jpg

R[m] = 2
w [rad/s] = 15
m [kg] = 5

I have been attempting this question but I have no idea as to where to start? If anyone could give me a hand that would be great.

 

[NascentOxygen]

Hi GaryTravis. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

Can you calculate the speed (magnitude and direction) of the stone at point A?

 

[GaryTravis]

Hey NascentOxygen, thanks for the welcome :D

To my knowledge the speed (in this case I'm assuming tangential speed.) is v=rw. So in this case v=2*15=30m/s. However I'm not certain if this is the right method.

Edit: As it turns out when i previously attempted the question i did not use this method (awkward...) but I have solved the question thanks for your assistance :D (I would never have double checked that equation if you didn't ask...)

 

[j_o_h_n]

Is there any chance someone could elaborate on this question?
I have a similar one and don't understand how finding speed could indicate the time...
Thank you!