21.The string of a pendulum is horizontal. The mass of the bob attached to it is m. Now the string is released. The tension in the string in the lowest position is

22.A coin placed on a gramophone record rotating at 33 r. p. m. files off the record, if it is placed at a distance of more than 16 cm from the axis of rotation. If the record is revolving at 66 r. p. m., the coin will fly off if it is placed at a distance not less than

23.The masses of two uniform discs are in the ratio 1 : 2 and their diameters in the 2 : 1. The ratio of their moments of inertia about the axes passing through their respective centres and perpendicular to their planes is

24.A nearly massless rod is pivoted at one end so that it can swing freely as a pendulum. Two masses 2m and m are attached to it at distance b and 3b respectively from the pivot. The rod is held horizontal and then released. The angular acceleration of the rod at the instant it is released is

25.A chain of 125 links is 1.25 m long and has a mass of 2 kg. With the ends fastened together, it is set rotating at 3000 rev/ min. The centripetal force on each link is