A load of 500 kg was lifted through a distance of 13 cm. by an effort of 25 kg which moved through a distance of 650 cm. The efficiency of the lifting machine is

A string of length 90 cm is fastened to two points A and B at the same level 60 cm apart. A ring weighing 120 g is slided on the string. A horizontal force P is applied to the ring such that it is in equilibrium vertically below B. The value of P is :

u_{1} and u_{2} are the velocities of approach of two moving bodies in the same direction and their corresponding velocities of separation are v_{1} and v_{2}. As per Newton's law of collision of elastic bodies, the coefficient of restitution (e) is given by