A block of mass m slides along a frictionless surface as shown in the figure. If it is releases from rest from A what is its speed at B?

Explanation

Take the block+ the earth as th system. Only the block moves, so only the work done on the block will contribute to the gravitatioN/A potential energy. As it descends through a height h between A and B, the potential energy decreses by mgh. The normal contact force N on the block by the surface does no work as it is perpendicular to its velocity. No exterN/Al force does any work on the system. Hence,
increase is kinetic energy = decrease in potential energy
`or, 1/2 mv^2=mgh or, v=sqrt(2gh)`