A \(35-\mathrm{kg}\) child stands on the edge of a \(400-\mathrm{kg}\) playground merry-go-round that is turning at the rate of 1 rev every \(2.2 \mathrm{~s}\). He then walks to the center of the platform. If the radius of the platform is \(1.5 \mathrm{~m}\), what is its rotational speed once he arrives at the center?