Question

a swimmer is able to swim in a forward direction in a swimming pool only when he is pushing the water in the backward direction . Why

Answer 1

due to newtons 3rd law of motion

Answer 2

According to Newtons third law of motion action = reaction . Because when swimmer push the water in backward direction which is action force , water also exerts equal and opposite force on swimmer that is reaction force . So the swimmer can able to swim .