A car mass 600kg is moving at speed of 20m/s . It collides with a stationary car of mass 900kg. If the first car bounces back at 4m/s at what speed does the second car move after the collision
The second car will move at 16m/s after the collision. This can be calculated using the equation of conservation of momentum.
Momentum before collision = Momentum after collision
600kg x 20m/s + 900kg x 0m/s = 600kg x 4m/s + 900kg x v
v = 16m/s
Bounces BACK (negative velocity)
600kg x 20m/s + 900kg x 0m/s = -600kg x 4m/s + 900kg x v
(answered forgot to type - sign )
so
12000 = -2400 + 900 v
900 v = 14400
v = 16