The velocity ratio of a differential pulley block with D and d as the diameters of larger and smaller pulley, is

The total momentum of a system of masses (i. e. moving bodies) in any one direction remains constant, unless acted upon by an external force in that direction. This statement is called

A machine having an efficiency less than 50%, is known as

The centre of gravity of a trapezium with parallel sides a and b lies at a distance of y from the base b, as shown in the below figure. The value of y is

Two bodies of masses m₁,and m₂ are hung from the ends of a rope, passing oyer a frictionless pulley as shown in the figure below. The acceleration of the string will be