Calculating Angular Velocity of Disk w/ Angular Momentum

[srecko97]

Homework Statement

There is a man walking on a disk with mass 70 kg and speed 4 m/s. He walks on a circle with radius 1,5 m. How fast does the disk (mass 200 kg and radius 2 m) under him rotates (need to calculate angular velocity)[/B]

Homework Equations

angular momentum = J * w (J-moment of inertia, w, angular velocity)

The Attempt at a Solution

(J_disk) * (w_disk) = (J_man) * (w_man)
1/2 MR^2 *(w_disk) = (mr^2* ( v_man)) / r
(w_disk) = mr(v_man) / MR^2
(w_disk) =1,05 /s

What am I doing wrong?

 

[srecko97]

I have already solved it. It is so so easy (I knew that before, that is why I was asking here, as I was sure that my answer was correct). I did not see that it was written that the velocity (4m/s) meant the velocity of a man towards the disk, not towards the observer somewhere out of the disk.