Question

why heat energy is necessary to melt a solid ? what is heat energy called

Answer 1

heat energy is used to melt a solid as dis heat energy increases d kinetic energy n thus breaks d bond bet d particles of a substances. this increases d speed of melting n d substance melts quickly. this heat is d hidden heat energy ie called latent heat.

Answer 2

heat energy is necessary to melt a solid because it increase the kinetic energy of the particles. As the kinetic energy of particles increases ,the bonding between the particles start  breaking and become free and start moving. As we know that moving of the particle cause the change in the  state of matter.Solid particles are very rigid, bu on applying heat the particles become loose and start moving and hence solid change into the liquid.
Further Heat energy is also called thermal energy.