Two weights are hanged via rope through movable block. Weights and block have mass. Rope is massless. Mass of one weight is bigger from second one. In moment weights start moving. One weight moves to up. Second weight moves down. Movement take place in gravity field. There is no friction between rope and block surface. We assume that air resist doesn't exist. Because there is no friction on block's surface no heat is released. During block's motion rotate around axis in its middle. Block is a roller. Subject of example is to find acceleration of weight which moves down.