Question

A large horizontal circular platform (M=143.1 kg, r=3.01 m) rotates about a frictionless vertical axle. A student (m=75.3 kg) walks slowly from the rim of the platform toward the center. The angular velocity ω of the system is 2.10 rad/s when the student is at the rim. Find ω (in rad/s) when the student is 2.89 m from the center.

Answer 1

conservation of angular momentum (the figure skater spins faster when she pulls her arms in

I1 omega1 = I2 omega2

I of platform = (1/2)(143.1)(3.01)^2
original I of student = m r^2 = 75.3(3.01)^2
final I of student = 75.3(2.89)^2

Answer 2

something is wrong in the answer, can you explain it again please?..

Answer 3

Ok,
Original I = (1/2)(143.1)(3.01^2 + 75.3*(3.01)^26
= 648 + 682 = 1330 kg m^2

Final I = 648 + 75.3(2.89)^2 = 1276

1330 (2.1) = 1276 omega
so
omega = 2.19 radians/second

Answer 4

Thank you very much.