Question

Give reason 1. A swimmer pushes water backwards.

Answer 1

According to newton's 3rd law of motion in each and every action there is an equal and opposite force. So if he push the water backwards then according to the above principle or law he will be able to move forward.

Answer 2

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A swimmer pushes a force on water backwards and then the pushed water give the buoyancy uplift and try to move the body forward. And so that the swimmer able to move forward in his way.