ICA8 - How fast are these objects moving immediately after the collision?

Question

A 1200 kg car moving to the right at 15 m/s collides with the back of a 2500 kg truck moving at 4 m/s, also to the right. After the collision, the two objects are stuck together.

Answer 1

m₁v₁ + m₂v₂ = (m₁ + m₂)v; v = (m₁v₁ + m₂v₂)/(m₁ + m₂) = (1200kg·15m/s + 2500kg·4m/s)/(1200kg + 2500kg) = 7.57 m/s