1. The problem statement, all variables and given/known data Using the formulae for potential energy and kinetic energy, find the speed that a tennis ball hits the ground when dropped from a height of 20m. With reference to the principle of conservation of energy, explain why you could use these equations and what assumptions you have made. 2. Relevant equations KE = 1/2mv^2 PE = mgh 3. The attempt at a solution The first part I think I'm ok with. The tennis ball is dropped therefore no KE only PE. PE = 9.8 x 20 = 196 Joules. It is the second part that I don't really understand. What is it asking me? Can somebody maybe re-frase this part of the question. Thank you.