A flat uniform circular disk (radius = 2.50 m, mass = 1.00 102 kg) is initially stationary. The disk is free to rotate in the horizontal plane about a frictionless axis perpendicular to the center of the disk. A 55.0-kg person, standing 1.10 m from the axis, begins to run on the disk in a circular path and has a tangential speed of 2.80 m/s relative to the ground.

(a) Find the resulting angular speed of the disk (in rad/s) and describe the direction of the rotation.

(b) Determine the time it takes for a spot marking the starting point to pass again beneath the runner's feet.

Question

A flat uniform circular disk (radius = 2.50 m, mass = 1.00  102 kg) is initially stationary. The disk is free to rotate in the horizontal plane about a frictionless axis perpendicular to the center of the disk. A 55.0-kg person, standing 1.10 m from the axis, begins to run on the disk in a circular path and has a tangential speed of 2.80 m/s relative to the ground.

(a) Find the resulting angular speed of the disk (in rad/s) and describe the direction of the rotation.
  
(b) Determine the time it takes for a spot marking the starting point to pass again beneath the runner's feet.

anonymous · Answer

the direction of rotation would be opposite to the runneres direction of motion as the runner pushes the disc to move himself forward(action on disc reaction by disc )
and when you get to know the angular velocity,
to know the

anonymous · Answer

b) part,distance is 2pi*r circumference(with radius=1.10m)
speed=2.8m/s u will get the time.i think..........