Physics
posted by Please Help!!! .
no matter how i work it out, i keep getting the wrong answers. please help!!! i only have two more submissions before it closes on me.
A sample of blood is placed in a centrifuge of radius 14.0 cm. The mass of a red blood cell is 3.0 x 10^16 kg, and the magnitude of the force acting on it as it settles out of the plasma is 4.0 x 10^11 N. At how many revolutions per second should the centrifuge be operated?

r = .14 meter
w = omega, angular rate in radians/sec
Ac = w^2 r
F = m Ac
4*10^11 = 3 *10^16 (w^2)(.14)
w^2 = 9.52 * 10^5 = 95.2 * 10^4
w = 9.76 * 10^2 radians/second
rev = 2 pi radians
976 rad/s * 1 rev/2pi rad = 155 rev/s