Answers by visitors named: Bastian

If the equation you're using is (1/2)M*V^2= J and you know J is o.4 just fill in the velocity(speed) and work it out. Here's how I worked it: (1/2)M*4^2 = 0.4 (change the numbers around) (Now it looks like:) 0.4/4^2/(1/2) = M (divide 0.4 by 4^2) 0.4/4^2 = 0.025 (then the answer by 1/2) 0.025/(1/2) = 0.050 or 0.05 so your answer is that the mass of the ball Lance threw is 0.05-kg.