How much would the earth "recoil" or move if...(energy/collision?) 1. The problem statement, all variables and given/known data all 6.5 billion people in the world with an average mass of 70kg, simultaneously jumped off of a 4 meter high platform. What energy would be imparted on the earth assuming people don't bend their knees when landing? 2. Relevant equations E_f = E_i and possibly inelastic collision assuming that people keep their knees locked when landing and bones don't break!: m1v1 + m2v2 = (m1 + m2)Vf 3. The attempt at a solution I can do the energy imparted part---> (1/2)mv^2 = mgh to find velocity of people then plug v into --> (1/2)mv^2 to find the Energy that would imparted on earth. I'm having a tough time figuring out how much the earth would actually "recoil" or move?? Will it even move at all?