In a skating stunt known as crack-the-whip, a number of skaters hold hands and form a straight line. They try to skate so that the line rotates about the skater at one end, who acts as the pivot. The skater farthest out has a mass of 80.0 kg and is 6.40 m from the pivot. He is skating at a speed of 6.50 m/s. Determine the magnitude of the centripetal force that acts on him.