21) A hoop of radius 3 m weighs 100 kg. It rolls along a horizontal floor so that at its centre of mass has a speed of 200 mm/sec, . The work required to stop the hoop is

22) A solid cylinder of mass M and radius R rolls down an inclined plane without slipping. The acceleration of center of mass of rolling cylinder is:{where ′g′ is acceleration due to gravity and 0 is inclination of plane with horizontal.}

23) A solid sphere of mass M and radius R rolls down a plane inclined at 0 with the horizontal. The acceleration of sphere is { where g is acceleration due to gravity}

24) A cylinder will slip on an inclined plane of inclination 0 if the coefficient of static friction between plane and cylinder is

25) Rate of change of angular momentum is equal to