physics
posted by Mary .
a 2kg car moving towards the right at 4 m/s collides head on with a 8 kg car moving towards the left at 2 m/s and they stick together. After the collision, the velocity of the combined boides is

Total momentum
= 2kg*4m/s + 8kg*(2m/s)
= 8 kgm/s
Final velocity for an inelastic collision
= 8 kgm/s / (2kg+8kg)
= 0.8 m/s
Since the velocity is negative, the final velocity is towards the left. 
Moving At 20m/s,a car with a mass of 7.0x10^2kg collides with a stationary truck with a mass of 1.4x10^3 kg. If the two vehicles stick together resulting from the collision, what is the velocity of the combined car and truck?

If a 10g bullet is fired from a 2000g rifle with a velocity of 500m/s at what velocity does the rifle recoil against the shooters shoulder??