posted by Daniel .
A 1230 kg car drives along a city street at 31.0 miles per hour, and a baseball has a mass of 0.142 kg. What speed must the baseball have if its momentum is to be equal in magnitude to that of the car? Give your result in miles per hour.
You have mass and velocity of car (lets designate that m1 and v1) and mass of ball (lets say that's m2). Solve for v2.