If the ball has a m of 50.0g, what is the ball's kinetic energy in joules?

The formula for Kinetic Energy of an object is KE = 1/2*m of object*velocity^2 The first thing you want to do is to convert 50.0 grams to .05 kg. Then convert 49.81 cm/s to .4981m/s Then you just plug the numbers into the formula. KE = 1/2*.05*(.4981)^2. Your KE in Joules, should be equal to .006J