Newton's First Law: An object at rest stays at rest an object in motion stays in motion unless acted on by an outside force. Even after the engine of the car is turned off, it continues to run on inertia and will not stop unless external forces like friction and drag slows it down and petsit to a complete stop.
Newton's Second Law: Force = Mass x Acceleration. (F=ma) The girl is applying a force of 5 newtons on the tennis ball and it is accelerating at a speed of 100m/s/s. The mass of the ball is 0.05 kg so the mass multiplied by the acceleration is the force. (0.05 x 100 = 5)
Newton's Third Law: For every action there is an equal and opposite reaction. The swimmer is pushing on the water with a force of 100 N and the water is also pushing him with the same force as the law says. Therefore he stays where he is.