Dear Student

It is because of newton's 3rd law

Every action has equal and opposite reaction.

Ball exert a force on wall in turn wall also exert same amount of force on ball.

All the best.                                                           

AKASH GOYAL

AskiitiansExpert-IIT Delhi

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A ball has kinetic energy when thrown towards wall

now  after collision with the wall the next motion depends on how the energy is transferred and where, because energy is always conserved and can't just disappear

the wall of course doesnt move and no sufficient heat is produced  to compensate loss of kinetic energy

hence ball has to continue moving but by newtonian mechanics it is clear that it will move backwards coz wall exerts equal n opp. force on it

so ball bounces backwards and if it is perfectly rigid it will do so with the initial speed