A1 kilogram ball has 8 joules of kinetic energy. what is the speed

                                 Kinetic energy = (1/2) x (mass) x (speed)²

                                       8 joules  =  (1/2 x 1 kg) x (speed)²

Divide each side by 1/2kg :  8 joules / 0.5 kg  =  speed²

Take the square root of each side:    

                 speed = √[ (8 kg-m²/sec²) / (0.5 kg) ] 

                           =  √ (8 m²/sec²)

                           =  √8   m/s  =  2.83 m/s  (rounded)