Givens: m=20kg r=2.0m L=360 kg m^2/s
Unknown: Speed . (But there are two "types of speed" which are angular speed and linear speed and ARE DIFFERENT)
Formulas: L=Iω Angular momentum = inertia x angular velocity (L=Iω)
I=mr^2; ω=v/r
Therefore, L=r^2m * v/r = rmv
L=rmv
360=20*2*v
360/(20*2) =v
360/40= v
v=9m/s (linear tangent speed)
Angular velocity ω= v/r
ω= 9/2
ω= 4.5rads/s (angular speed)
In other words, both 9 and 4.5 should be right if explained correctly.