text: physics help? an 845 kg dragster accelerates from rest to 100 km/h in .90 seconds.  what is the change in the momentum of the car? what is the average force exerted on the car? what exerts that force?  a 95 kg fullback, running at 8.2 m/s, collides in midair with a 128 kg defensive tackle moving in the opposite direction. both players end up with zero speed.  what was the fullback's momentum before the collision? what was the change in the fullback's momentum? what was the change in the tackle's momentum? what was the tackle's original momentum? how fast was the tackle moving originally?  ball a, rolling west at 3.0 m/s has a mass of 1 kg. ball b has a mass of 2 kg and is stationary. after colliding with ball b ball a moves south at 2 m/s calculate the momentum and velocity of ball b after the collision change in momentum=mv  where m=mass and v=velocity.  plug it in to the equation.  average 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.  use the equations for the second equation.  use common sense for the questions that dont' involve equations.  use the conservation of momentum theory to do the last problem.    (ma)(va)+(mb)(vb)= (ma)(va2)+(mb)(vb2)   i'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.    plug in the knowns, solve for the unknowns.