21.A partly hanging uniform chain of length L is resting on a rough horizontal table. l is the maximum possible length that can hang in equilibrium. The coefficient of friction between the chain and table is

22.A weight w is suspended from the midpoint of a rope, whose ends are at the same level. In order to make the rope perfectly horizontal, the force applied to each of its ends must be:

23.Water jet issues water from a nozzle of 2 square cm cross-section with velocity 30 cm/s and strikes a plane surface placed at right angles to the jet. The force exerted on the plane is:

24.A box weighing 20 N is moved along a horizontal surface through a distance of 25 m. If the coefficient of friction is 0.4, the work done against friction is

25.A block of mass 3 kg is in contact with a block of mass 2 kg. Both the blocks rest on a frictionless floor. A horizontal force of 10 N is applied to push the block of mass 3 kg. The force with which the first block pushes the second block is