An athlete prepares to throw a 2.0-kilogram discus. his arm is 0.75 meters long. he spins around several times with the discus at the end of his out-stretched arm so that the discus reaches a velocity of 5.0 m/s. what is the centripetal force acting on the discus?

The centripetal force acting on ball will be = mass x radial acceleration
radial acceleration = v²/radius of the discuss performing circular motion
                              =  5²/0.75 = 33.33 m/s²

Therefore, centripetal force = mass x radial acceleration = 2 x 33.33
                                                                                          = 66.66 N. 

Newton's first law of motion states that an object at rest remains at rest and an object in motion remains in motion with the same velocity unless acted upon by what we call an unbalanced force. The force of gravity pulling down is balanced by the force of my kitchen table pushing up on my cup of coffee.