text: change in momentum=mv  where m=mass and v=velocity.  plug it in to the equation.\n\naverage force=ma  where m=mass and a=acceleration.  since acceleration is not giving in the problem, you must solve for it.  subtract starting velocity from ending velocity and divide it by the time.\n\nuse the equations for the second equation.  use common sense for the questions that dont' involve equations.\n\nuse the conservation of momentum theory to do the last problem.  \n\n(mA)(vA)+(mB)(vB)=\n(mA)(vA2)+(mB)(vB2)\n\n\ni'm sorry that looks hairy, i will explain... the mass of ball A times the BEGINNING velocity of ball A, plus the mass of ball B times the velocity of ball B equals the mass of ball A times the ENDING velocity of ball a plus the mass of ball B times the ENDING velocity of ball B.  \n\nplug in the knowns, solve for the unknowns.