Mechnaical energy is always constant. Is it true?

What is energy?

The unit of energy is

When a charged particle moves in a magnetci field does the kinetic energy always remains constant?

Every real number is always rational

Show that the amount of kinetic energy always decreases in perfectly inelastic collision in one dimension.

Read each statement below carefully and state, with reasons, if it is true or false The net acceleration of a particle in circular motion is always along the radius of the circle towards the centre

Show that the sum of potential and kinetic energy of a body falling freely under gravity is constant.What happens to theses energies when the body hits the ground?