21.The condilion for a lifting machine to be reversible is that its efficiency should be

22.A cable loaded with 10 kN/m of span is stretched between supports in the same horizontal line 100 m apart. If the central dip is 10 m, then the maximum and minimum pull in the cable respectively are

23.A shell of mass 100 kg travelling with a velocity of 10 m/sec breaks into two equal pieces during an explosion which provides an extra kinetic energy of 20000 Joules. If the pieces continue to move in the same direction as before, then the speed of the faster one must be

24.If a flywheel increases its speed from 10 rpm to 20 rpm in 10 seconds, then its angular acceleration is