A)a skater is spinning about a fixed vertical axis when she lifts her arms above her head; her moment of inertia about the axis of rotation drops from 10.0 kg m2 to 5.0 kg m2. by what factor does her rotational kinetic energy change? (you may assume that her angular momentum is conserved.) b) mars is approximately twice as far away from the sun as venus, and has one-eighth of venus' mass. what is the ratio of the orbital moment of inertia of mars to that of venus, about an axis through the sun, perpendicular to the plane of the solar system? (you may assume that the orbits are circular and coplanar.) c)two very thin concentric circular hoops of mass 0.20 kg and 0.30 kg have radii of 1.5 m and 0.90 m respectively. they are connected by rigid links of negligible mass such that they lie in the same plane. calculate the system's moment of inertia about an axis through the centre and perpendicular to the plane of the hoops. d)a child of mass 35 kg is sitting on the seat of a swing, suspended from a rigid bar on ropes that are 2.0 m long. calculate the moment of inertia of the child with respect to the bar about which the swing rotates.