Newton's second law and law of conservation of momentum

                                                    law of conservation of momentum
refer site http://simplethinking.com/teaching/newtonlaws_files/image002.jpg
law of conservation of momentum state's that the total momentum of a system will be constant that is the momentum before collision will be equal to the momentum after collision in the absence of an external force .this law is accurate only in the absence of external force (vacuum) .in air frictional force,gravitational force,etc.are experienced on the body.

                               Newton's second law of motion

                              newton's second law of motion state's that the rate of change of momentum is directly proportional to the external unbalanced force acting on a body .
initial momentum =mu
final momentum=mv
so rate of change of momentum =(mv-mu)/t
                                                =(m(v-u))/t
                                             f  =m x a(directly proportional)   
                                             
                              1. a body which is having mass 10kg moves with a velocity of 5m/s  hits another body which has the same mass and which is at rest. what is the momentum of the first body after collision and before collision ?
answer: momentum before collision (p) =mass x velocity
p=10kg x 5m/s =50kgm/s
  momentum after collision
 mass=5kg
velocity=0m/s
  momentum after collision =5 x 0=0 kgm/s