Question

Explain in a clear sentence or two how the mechanical energy will change as a block slides down an inclined track, where friction can no longer be ignored. (i.e., does the mechanical energy increase, stay constant, or decrease and why?)

Answer 1

Mechanical energy is the sum of the potential and kinetic energies in a system.Change in total mechanical energy is equal to work done by non conservative force .This kind of work done by non conservative force like friction is negative as friction and displacement are in opposite direction ,so change in mechanical energy will be negative that means mechanical energy decreases .

when there is no friction total mechanical energy remains constant it just transforms from potential energy at the top of the incline to kinetic energy at bottom of the inclined plane . since there is no friction work done by non conservative forces are zero so change in total mechanical energy is zero