Question

A 189.3-kg and a 258.9-kg cart approach each other on a horizontal air track. They collide and stick together. After the collision their total kinetic energy is 1142.5 J. What is the speed after the collision

Answer 1

$$E_k=\frac{mv^2}{2}$$ $$v=\sqrt{2E_k/m}\\ =\sqrt{2*1142.5/(189.3+258.9)}=2.258\:\rm m/s$$