A dad and his kid are riding bumper cars at the amusement park.  The dad and his car weigh 200 kg, combined, and are travelling at 1 m/s at the time of collision.  The kid and their car weigh 125 kg, and are traveling -2 m/s at the time of collision. Step 1. This collision is Elastic.
Step 2:  Before the collision, what is the momentum of...
Dad   kg * m/s
Kid   kg * m/s  
Step 3: After the collision, what is the momentum of...
Dad   kg * m/s
Kid   kg * m/s    
Step 4: Using v = p/m, what is the final velocity of...
Dad   m/s
Kid   m/s​